GETATTRLIST(2) BSD System Calls Manual GETATTRLIST(2)NAME
getattrlist, fgetattrlist — get file system attributes
SYNOPSIS
#include <sys/attr.h>
#include <unistd.h>
int
getattrlist(const char* path, struct attrlist * attrList, void * attrBuf,
size_t attrBufSize, unsigned long options);
int
fgetattrlist(int fd, struct attrlist * attrList, void * attrBuf,
size_t attrBufSize, unsigned long options);
DESCRIPTION
The getattrlist() function returns attributes (that is, metadata) of file
system objects. getattrlist() works on the file system object named by
path, while fgetattrlist() works on the provided file descriptor fd. You
can think of getattrlist() as a seriously enhanced version of stat(2).
The functions return attributes about the specified file system object
into the buffer specified by attrBuf and attrBufSize. The attrList
parameter determines what attributes are returned. The options parameter
lets you control specific aspects of the function's behavior.
The getattrlist() and fgetattrlist() functions are only supported by cer‐
tain volume format implementations. For maximum compatibility, client
programs should use high-level APIs (such as the Carbon File Manager) to
access file system attributes. These high-level APIs include logic to
emulate file system attributes on volumes that don't support the calls.
Not all volumes support all attributes. See the discussion of
ATTR_VOL_ATTRIBUTES for a discussion of how to determine whether a par‐
ticular volume supports a particular attribute.
Furthermore, you should only request the attributes that you need. Some
attributes are expensive to calculate on some volume formats. For exam‐
ple, ATTR_DIR_ENTRYCOUNT is usually expensive to calculate on non-HFS
[Plus] volumes. If you don't need a particular attribute, you should not
ask for it.
The path parameter must reference a valid file system object. Read,
write or execute permission of the object itself is not required, but all
directories listed in the path name leading to the object must be search‐
able.
The attrList parameter is a pointer to an attrlist structure, as defined
by ⟨sys/attr.h⟩ (shown below). It determines what attributes are
returned by the function. You are responsible for filling out all fields
of this structure before calling the function.
typedef u_int32_t attrgroup_t;
struct attrlist {
u_short bitmapcount; /* number of attr. bit sets in list */
u_int16_t reserved; /* (to maintain 4-byte alignment) */
attrgroup_t commonattr; /* common attribute group */
attrgroup_t volattr; /* volume attribute group */
attrgroup_t dirattr; /* directory attribute group */
attrgroup_t fileattr; /* file attribute group */
attrgroup_t forkattr; /* fork attribute group */
};
#define ATTR_BIT_MAP_COUNT 5
The fields of the attrlist structure are defined as follows.
bitmapcount Number of attribute bit sets in the structure. In cur‐
rent systems you must set this to ATTR_BIT_MAP_COUNT.
reserved Reserved. You must set this to 0.
commonattr A bit set that specifies the common attributes that you
require. Common attributes relate to all types of file
system objects. See below for a description of these
attributes.
volattr A bit set that specifies the volume attributes that you
require. Volume attributes relate to volumes (that is,
mounted file systems). See below for a description of
these attributes. If you request volume attributes, path
must reference the root of a volume. In addition, you
can't request volume attributes if you also request file
or directory attributes.
dirattr A bit set that specifies the directory attributes that
you require. See below for a description of these
attributes.
fileattr A bit set that specifies the file attributes that you
require. See below for a description of these
attributes.
forkattr A bit set that specifies the fork attributes that you
require. Fork attributes relate to the actual data in
the file, which can be held in multiple named contiguous
ranges, or forks. See below for a description of these
attributes.
Unless otherwise noted in the lists below, attributes are read-only.
Attributes labelled as read/write can be set using setattrlist(2).
The attrBuf and attrBufSize parameters specify a buffer into which the
function places attribute values. The format of this buffer is suffi‐
ciently complex that its description requires a separate section (see
below). The initial contents of this buffer are ignored.
The options parameter is a bit set that controls the behaviour of the
functions. The following option bits are defined.
FSOPT_NOFOLLOW If this bit is set, getattrlist() will not follow
a symlink if it occurs as the last component of
path.
FSOPT_REPORT_FULLSIZE The size of the attributes reported (in the first
u_int32_t field in the attribute buffer) will be
the size needed to hold all the requested
attributes; if not set, only the attributes actu‐
ally returned will be reported. This allows the
caller to determine if any truncation occurred.
FSOPT_PACK_INVAL_ATTRS If this is bit is set, then all requested
attributes, even ones that are not supported by
the object or file system, will be returned.
Default values will be used for the invalid ones.
Requires that ATTR_CMN_RETURNED_ATTRS be
requested.
ATTRIBUTE BUFFER
The data returned in the buffer described by attrBuf and attrBufSize is
formatted as follows.
1. The first element of the buffer is a u_int32_t that contains the
overall length, in bytes, of the attributes returned. This size
includes the length field itself.
2. Following the length field is a list of attributes. Each attribute
is represented by a field of its type, where the type is given as
part of the attribute description (below).
3. The attributes are placed into the attribute buffer in the order
that they are described below.
4. Each attribute is aligned to a 4-byte boundary (including 64-bit
data types).
If the attribute is of variable length, it is represented in the list by
an attrreference structure, as defined by ⟨sys/attr.h⟩ (shown below).
typedef struct attrreference {
int32_t attr_dataoffset;
u_int32_t attr_length;
} attrreference_t;
This structure contains a 'pointer' to the variable length attribute
data. The attr_length field is the length of the attribute data (in
bytes). The attr_dataoffset field is the offset in bytes from the
attrreference structure to the attribute data. This offset will always
be a multiple of sizeof(u_int32_t) bytes, so you can safely access common
data types without fear of alignment exceptions.
The getattrlist() function will silently truncate attribute data if
attrBufSize is too small. The length field at the front of the attribute
list always represents the length of the data actually copied into the
attribute buffer. If the data is truncated, there is no easy way to
determine the buffer size that's required to get all of the requested
attributes. You should always pass an attrBufSize that is large enough
to accommodate the known size of the attributes in the attribute list
(including the leading length field).
Because the returned attributes are simply truncated if the buffer is too
small, it's possible for a variable length attribute to reference data
beyond the end of the attribute buffer. That is, it's possible for the
attribute data to start beyond the end of the attribute buffer (that is,
if attrRef is a pointer to the attrreference_t, ( ( (char *) attrRef ) +
attr_dataoffset ) > ( ( (char *) attrBuf ) + attrSize ) ) or, indeed, for
the attribute data to extend beyond the end of the attribute buffer (that
is, ( ( (char *) attrRef ) + attr_dataoffset + attr_datalength ) > ( (
(char *) attrBuf ) + attrSize ) ). If this happens you must increase the
size of the buffer and call getattrlist() to get an accurate copy of the
attribute.
COMMON ATTRIBUTES
Common attributes relate to all types of file system objects. The fol‐
lowing common attributes are defined.
ATTR_CMN_RETURNED_ATTRS An attribute_set_t structure which is used to
report which of the requested attributes were
actually returned. This attribute, when
requested, will always be the first attribute
returned. By default, unsupported attributes
will be skipped (i.e. not packed into the out‐
put buffer). This behavior can be over-ridden
using the FSOPT_PACK_INVAL_ATTRS option flag.
Only getattrlist(2) supports this attribute (
getdirentriesattr(2) and searchfs(2) do not
support it ).
ATTR_CMN_NAME An attrreference structure containing the name
of the file system object as UTF-8 encoded,
null terminated C string. The attribute data
length will not be greater than NAME_MAX + 1
characters, which is NAME_MAX * 3 + 1 bytes (as
one UTF-8-encoded character may take up to
three bytes).
ATTR_CMN_DEVID A dev_t containing the device number of the
device on which this file system object's vol‐
ume is mounted. Equivalent to the st_dev field
of the stat structure returned by stat(2).
ATTR_CMN_FSID An fsid_t structure containing the file system
identifier for the volume on which the file
system object resides. Equivalent to the
f_fsid field of the statfs structure returned
by statfs(2).
This value is not related to the file system ID
from traditional Mac OS (for example, the
filesystemID field of the FSVolumeInfo struc‐
ture returned by Carbon's FSGetVolumeInfo()
function). On current versions of Mac OS X
that value is synthesised by the Carbon File
Manager.
ATTR_CMN_OBJTYPE An fsobj_type_t that identifies the type of
file system object. The values are taken from
enum vtype in ⟨sys/vnode.h⟩.
ATTR_CMN_OBJTAG An fsobj_tag_t that identifies the type of file
system containing the object. The values are
taken from enum vtagtype in ⟨sys/vnode.h⟩.
ATTR_CMN_OBJID An fsobj_id_t structure that uniquely identi‐
fies the file system object within its volume.
The fid_generation field of this structure will
be zero for all non-root callers (effective UID
not 0). This identifier need not be persistent
across an unmount/mount sequence.
Some volume formats use well known values for
the fid_objno field for the root directory (2)
and the parent of root directory (1). This is
not a required behaviour of this attribute.
ATTR_CMN_OBJPERMANENTID An fsobj_id_t structure that uniquely identi‐
fies the file system object within its volume.
The fid_generation field of this structure will
be zero for all non-root callers (effective UID
not 0). This identifier should be persistent
across an unmount/mount sequence.
Some file systems (for example, original HFS)
may need to modify the on-disk structure to
return a persistent identifier. If such a file
system is mounted read-only, an attempt to get
this attribute will fail with the error EROFS.
ATTR_CMN_PAROBJID An fsobj_id_t structure that identifies the
parent directory of the file system object.
The fid_generation field of this structure will
be zero for all non-root callers (effective UID
not 0). Equivalent to the ATTR_CMN_OBJID
attribute of the parent directory. This iden‐
tifier need not be persistent across an
unmount/mount sequence.
On a volume that supports hard links, a multi‐
ply linked file has no unique parent. This
attribute will return an unspecified parent.
For some volume formats this attribute is very
expensive to calculate.
ATTR_CMN_SCRIPT (read/write) A text_encoding_t containing a
text encoding hint for the file system object's
name. It is included to facilitate the loss‐
less round trip conversion of names between
Unicode and traditional Mac OS script encod‐
ings. The values are defined in
⟨CarbonCore/TextCommon.h⟩. File systems that
do not have an appropriate text encoding value
should return kTextEncodingMacUnicode. See DTS
Q&A 1173 "File Manager Text Encoding Hints".
ATTR_CMN_CRTIME (read/write) A timespec structure containing
the time that the file system object was cre‐
ated.
ATTR_CMN_MODTIME (read/write) A timespec structure containing
the time that the file system object was last
modified. Equivalent to the st_mtimespec field
of the stat structure returned by stat(2).
ATTR_CMN_CHGTIME (read/write) A timespec structure containing
the time that the file system object's
attributes were last modified. Equivalent to
the st_ctimespec field of the stat structure
returned by stat(2).
ATTR_CMN_ACCTIME (read/write) A timespec structure containing
the time that the file system object was last
accessed. Equivalent to the st_atimespec field
of the stat structure returned by stat(2).
ATTR_CMN_BKUPTIME (read/write) A timespec structure containing
the time that the file system object was last
backed up. This value is for use by backup
utilities. The file system stores but does not
interpret the value.
ATTR_CMN_FNDRINFO (read/write) 32 bytes of data for use by the
Finder. Equivalent to the concatenation of a
FileInfo structure and an ExtendedFileInfo
structure (or, for directories, a FolderInfo
structure and an ExtendedFolderInfo structure).
These structures are defined in
⟨CarbonCore/Finder.h⟩.
This attribute is not byte swapped by the file
system. The value of multibyte fields on disk
is always big endian. When running on a little
endian system (such as Darwin on x86), you must
byte swap any multibyte fields.
ATTR_CMN_OWNERID (read/write) A uid_t containing the owner of
the file system object. Equivalent to the
st_uid field of the stat structure returned by
stat(2).
ATTR_CMN_GRPID (read/write) A gid_t containing the group of
the file system object. Equivalent to the
st_gid field of the stat structure returned by
stat(2).
ATTR_CMN_ACCESSMASK (read/write) A u_int32_t containing the access
permissions of the file system object. Equiva‐
lent to the st_mode field of the stat structure
returned by stat(2). Only the permission bits
of st_mode are valid; other bits should be
ignored, e.g., by masking with ~S_IFMT.
ATTR_CMN_NAMEDATTRCOUNT A u_int32_t containing the number of named
attributes of the file system object.
ATTR_CMN_NAMEDATTRLIST An attrreference structure containing a list of
named attributes of the file system object. No
built-in file systems on Mac OS X currently
support named attributes. Because of this, the
structure of this attribute's value is not yet
defined.
ATTR_CMN_FLAGS (read/write) A u_int32_t containing file flags.
Equivalent to the st_flags field of the stat
structure returned by stat(2). For more infor‐
mation about these flags, see chflags(2).
The order that attributes are placed into the
attribute buffer almost invariably matches the
order of the attribute mask bit values. The
exception is ATTR_CMN_FLAGS. If its order was
based on its bit position, it would be before
the ATTR_CMN_NAMEDATTRCOUNT /
ATTR_CMN_NAMEDATTRLIST pair, however, it is
placed in the buffer after them.
ATTR_CMN_USERACCESS A u_int32_t containing the effective permis‐
sions of the current user (the calling
process's effective UID) for this file system
object. You can test for read, write, and exe‐
cute permission using R_OK, W_OK, and X_OK,
respectively. See access(2) for more details.
ATTR_CMN_EXTENDED_SECURITY
A variable-length object (thus an attrreference
structure) containing a kauth_filesec struc‐
ture, of which only the ACL entry is used.
ATTR_CMN_UUID A guid_t of the owner of the file system
object. Analoguous to ATTR_CMN_OWNERID.
ATTR_CMN_GRPUUID A guid_t of the group to which the file system
object belongs. Analoguous to ATTR_CMN_GRPID.
ATTR_CMN_FILEID A u_int64_t that uniquely identifies the file
system object within its volume.
ATTR_CMN_PARENTID A u_int64_t that identifies the parent direc‐
tory of the file system object.
ATTR_CMN_FULLPATH An attrreference structure containing the full
path (resolving all symlinks) to the file sys‐
tem object as a UTF-8 encoded, null terminated
C string. The attribute data length will not
be greater than PATH_MAX. Inconsistent behavior
may be observed when this attribute is
requested on hard-linked items, particularly
when the file system does not support
ATTR_CMN_PARENTID natively. Callers should be
aware of this when requesting the full path of
a hard-linked item.
ATTR_CMN_ADDEDTIME A timespec that contains the time that the file
system object was created or renamed into its
containing directory. Note that inconsistent
behavior may be observed when this attribute is
requested on hard-linked items.
VOLUME ATTRIBUTES
Volume attributes relate to volumes (that is, mounted file systems). The
following volume attributes are defined.
ATTR_VOL_INFO For reasons that are not at all obvious, you
must set ATTR_VOL_INFO in the volattr field if
you request any other volume attributes. This
does not result in any attribute data being
added to the attribute buffer.
ATTR_VOL_FSTYPE A u_int32_t containing the file system type.
Equivalent to the f_type field of the statfs
structure returned by statfs(2). Generally not
a useful value.
ATTR_VOL_SIGNATURE A u_int32_t containing the volume signature
word. This value is unique within a given file
system type and lets you distinguish between
different volume formats handled by the same
file system. See ⟨CarbonCore/Files.h⟩ for more
details.
ATTR_VOL_SIZE An off_t containing the total size of the vol‐
ume in bytes.
ATTR_VOL_SPACEFREE An off_t containing the free space on the vol‐
ume in bytes.
ATTR_VOL_SPACEAVAIL An off_t containing the space, in bytes, on the
volume available to non-privileged processes.
This is the free space minus the amount of
space reserved by the system to prevent criti‐
cal disk exhaustion errors. Non-privileged
programs, like a disk management tool, should
use this value to display the space available
to the user.
ATTR_VOL_SPACEAVAIL is to ATTR_VOL_SPACEFREE as
f_bavail is to f_bfree in statfs(2).
ATTR_VOL_MINALLOCATION An off_t containing the minimum allocation size
on the volume in bytes. If you create a file
containing one byte, it will consume this much
space.
ATTR_VOL_ALLOCATIONCLUMP An off_t containing the allocation clump size
on the volume, in bytes. As a file is
extended, the file system will attempt to allo‐
cate this much space each time in order to
reduce fragmentation.
ATTR_VOL_IOBLOCKSIZE A u_int32_t containing the optimal block size
when reading or writing data. Equivalent to
the f_iosize field of the statfs structure
returned by statfs(2).
ATTR_VOL_OBJCOUNT A u_int32_t containing the number of file sys‐
tem objects on the volume.
ATTR_VOL_FILECOUNT A u_int32_t containing the number of files on
the volume.
ATTR_VOL_DIRCOUNT A u_int32_t containing the number of directo‐
ries on the volume.
ATTR_VOL_MAXOBJCOUNT A u_int32_t containing the maximum number of
file system objects that can be stored on the
volume.
ATTR_VOL_MOUNTPOINT An attrreference structure containing the path
to the volume's mount point as a UTF-8 encoded,
null terminated C string. The attribute data
length will not be greater than MAXPATHLEN.
Equivalent to the f_mntonname field of the
statfs structure returned by statfs(2).
ATTR_VOL_NAME (read/write) An attrreference structure con‐
taining the name of the volume as a UTF-8
encoded, null terminated C string. The
attribute data length will not be greater than
NAME_MAX + 1.
This attribute is only read/write if the
VOL_CAP_INT_VOL_RENAME bit is set in the volume
capabilities (see below).
ATTR_VOL_MOUNTFLAGS A u_int32_t containing the volume mount flags.
This is a copy of the value passed to the flags
parameter of mount(2) when the volume was
mounted. Equivalent to the f_flags field of
the statfs structure returned by statfs(2).
ATTR_VOL_MOUNTEDDEVICE An attrreference structure that returns the
same value as the f_mntfromname field of the
statfs structure returned by statfs(2). For
local volumes this is the path to the device on
which the volume is mounted as a UTF-8 encoded,
null terminated C string. For network volumes,
this is a unique string that identifies the
mount. The attribute data length will not be
greater than MAXPATHLEN.
ATTR_VOL_ENCODINGSUSED An unsigned long long containing a bitmap of
the text encodings used on this volume. For
more information about this, see the discussion
of encodingsBitmap in DTS Technote 1150 "HFS
Plus Volume Format".
ATTR_VOL_CAPABILITIES A vol_capabilities_attr_t structure describing
the optional features supported by this volume.
See below for a discussion of volume capabili‐
ties.
ATTR_VOL_UUID A uuid_t containing the file system UUID. Typ‐
ically this will be a version 5 UUID.
ATTR_VOL_ATTRIBUTES A vol_attributes_attr_t structure describing
the attributes supported by this volume. This
structure is discussed below, along with volume
capabilities.
DIRECTORY ATTRIBUTES
The following directory attributes are defined.
ATTR_DIR_LINKCOUNT A u_int32_t containing the number of hard links
to the directory; this does not include the
historical "." and ".." entries. For file sys‐
tems that do not support hard links to directo‐
ries, this value will be 1.
ATTR_DIR_ENTRYCOUNT A u_int32_t containing the number of file sys‐
tem objects in the directory, not including any
synthetic items. The historical "." and ".."
entries are also excluded from this count.
ATTR_DIR_MOUNTSTATUS A u_int32_t containing flags describing what's
mounted on the directory. Currently the only
flag defined is DIR_MNTSTATUS_MNTPOINT, which
indicates that there is a file system mounted
on this directory.
Requested directory attributes are not returned for file system objects
that are not directories.
FILE ATTRIBUTES
The following file attributes are defined.
ATTR_FILE_LINKCOUNT A u_int32_t containing the number of hard links
to this file. Equivalent to the st_nlink field
of the stat structure returned by stat(2).
ATTR_FILE_TOTALSIZE An off_t containing the total number of bytes
in all forks of the file (the logical size).
ATTR_FILE_ALLOCSIZE An off_t containing a count of the bytes on
disk used by all of the file's forks (the phys‐
ical size).
ATTR_FILE_IOBLOCKSIZE A u_int32_t containing the optimal block size
when reading or writing this file's data.
ATTR_FILE_CLUMPSIZE A u_int32_t containing the allocation clump
size for this file, in bytes. As the file is
extended, the file system will attempt to allo‐
cate this much space each time in order to
reduce fragmentation. This value applies to
the data fork.
ATTR_FILE_DEVTYPE (read/write) A u_int32_t containing the device
type for a special device file. Equivalent to
the st_rdev field of the stat structure
returned by stat(2).
ATTR_FILE_FILETYPE A u_int32_t that whose value is reserved.
Clients should ignore its value. New volume
format implementations should not support this
attribute.
ATTR_FILE_FORKCOUNT A u_int32_t containing the number of forks in
the file. No built-in file systems on Mac OS X
currently support forks other than the data and
resource fork.
ATTR_FILE_FORKLIST An attrreference structure containing a list of
named forks of the file. No built-in file sys‐
tems on Mac OS X currently support forks other
than the data and resource fork. Because of
this, the structure of this attribute's value
is not yet defined.
ATTR_FILE_DATALENGTH An off_t containing the length of the data fork
in bytes (the logical size).
ATTR_FILE_DATAALLOCSIZE An off_t containing a count of the bytes on
disk used by the data fork (the physical size).
ATTR_FILE_DATAEXTENTS An extentrecord array for the data fork. The
array contains eight diskextent structures
which represent the first eight extents of the
fork.
This attributes exists for compatibility rea‐
sons. New clients should not use this
attribute. Rather, they should use the
F_LOG2PHYS command in fcntl(2).
In current implementations the value may not be
entirely accurate for a variety of reasons.
ATTR_FILE_RSRCLENGTH An off_t containing the length of the resource
fork in bytes (the logical size).
ATTR_FILE_RSRCALLOCSIZE An off_t containing a count of the bytes on
disk used by the resource fork (the physical
size).
ATTR_FILE_RSRCEXTENTS An extentrecord array for the resource fork.
The array contains eight diskextent structures
which represent the first eight extents of the
fork.
See also ATTR_FILE_DATAEXTENTS.
File attributes are used for any file system object that is not a direc‐
tory, not just ordinary files. Requested file attributes are not
returned for file system objects that are directories.
FORK ATTRIBUTES
Fork attributes relate to the actual data in the file, which can be held
in multiple named contiguous ranges, or forks. The following fork
attributes are defined.
ATTR_FORK_TOTALSIZE An off_t containing the length of the fork in
bytes (the logical size).
ATTR_FORK_ALLOCSIZE An off_t containing a count of the bytes on
disk used by the fork (the physical size).
Fork attributes are not properly implemented by any current Mac OS X vol‐
ume format implementation. We strongly recommend that client programs do
not request fork attributes. If you are implementing a volume format,
you should not support these attributes.
VOLUME CAPABILITIES
Not all volumes support all features. The ATTR_VOL_CAPABILITIES
attribute returns a vol_capabilities_attr_t structure (shown below) that
indicates which features are supported by the volume.
typedef u_int32_t vol_capabilities_set_t[4];
#define VOL_CAPABILITIES_FORMAT 0
#define VOL_CAPABILITIES_INTERFACES 1
#define VOL_CAPABILITIES_RESERVED1 2
#define VOL_CAPABILITIES_RESERVED2 3
typedef struct vol_capabilities_attr {
vol_capabilities_set_t capabilities;
vol_capabilities_set_t valid;
} vol_capabilities_attr_t;
The structure contains two fields, capabilities and valid. Each consists
of an array of four elements. The arrays are indexed by the following
values.
VOL_CAPABILITIES_FORMAT This element contains information about
the volume format. See
VOL_CAP_FMT_PERSISTENTOBJECTIDS and so
on, below.
VOL_CAPABILITIES_INTERFACES This element contains information about
which optional functions are supported
by the volume format implementation.
See VOL_CAP_INT_SEARCHFS and so on,
below.
VOL_CAPABILITIES_RESERVED1 Reserved. A file system implementation
should set this element to zero. A
client program should ignore this ele‐
ment.
VOL_CAPABILITIES_RESERVED2 Reserved. A file system implementation
should set this element to zero. A
client program should ignore this ele‐
ment.
The valid field contains bit sets that indicate which flags are known to
the volume format implementation. Each bit indicates whether the con‐
tents of the corresponding bit in the capabilities field is valid.
The capabilities field contains bit sets that indicate whether a particu‐
lar feature is implemented by this volume format.
The following bits are defined in the first element (indexed by
VOL_CAPABILITIES_FORMAT) of the capabilities and valid fields of the
vol_capabilities_attr_t structure.
VOL_CAP_FMT_PERSISTENTOBJECTIDS If this bit is set the volume format
supports persistent object identifiers
and can look up file system objects by
their IDs. See ATTR_CMN_OBJPERMANENTID
for details about how to obtain these
identifiers.
VOL_CAP_FMT_SYMBOLICLINKS If this bit is set the volume format
supports symbolic links.
VOL_CAP_FMT_HARDLINKS If this bit is set the volume format
supports hard links.
VOL_CAP_FMT_JOURNAL If this bit is set the volume format
supports a journal used to speed recov‐
ery in case of unplanned restart (such
as a power outage or crash). This does
not necessarily mean the volume is
actively using a journal.
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_FMT_JOURNAL_ACTIVE If this bit is set the volume is cur‐
rently using a journal for speedy recov‐
ery after an unplanned restart. This
bit can be set only if
VOL_CAP_FMT_JOURNAL is also set.
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_FMT_NO_ROOT_TIMES If this bit is set the volume format
does not store reliable times for the
root directory, so you should not depend
on them to detect changes, identify vol‐
umes across unmount/mount, and so on.
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_FMT_SPARSE_FILES If this bit is set the volume format
supports sparse files, that is, files
which can have 'holes' that have never
been written to, and thus do not consume
space on disk. A sparse file may have
an allocated size on disk that is less
than its logical length (that is,
ATTR_FILE_ALLOCSIZE <
ATTR_FILE_TOTALSIZE ).
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_FMT_ZERO_RUNS For security reasons, parts of a file
(runs) that have never been written to
must appear to contain zeroes. When
this bit is set, the volume keeps track
of allocated but unwritten runs of a
file so that it can substitute zeroes
without actually writing zeroes to the
media. This provides performance simi‐
lar to sparse files, but not the space
savings.
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_FMT_CASE_SENSITIVE If this bit is set the volume format
treats upper and lower case characters
in file and directory names as differ‐
ent. Otherwise an upper case character
is equivalent to a lower case character,
and you can't have two names that differ
solely in the case of the characters.
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_FMT_CASE_PRESERVING If this bit is set the volume format
preserves the case of file and directory
names. Otherwise the volume may change
the case of some characters (typically
making them all upper or all lower
case). A volume that sets
VOL_CAP_FMT_CASE_SENSITIVE must also set
VOL_CAP_FMT_CASE_PRESERVING.
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_FMT_FAST_STATFS This bit is used as a hint to upper lay‐
ers (specifically the Carbon File Man‐
ager) to indicate that statfs(2) is fast
enough that its results need not be
cached by the caller. A volume format
implementation that caches the statfs(2)
information in memory should set this
bit. An implementation that must always
read from disk or always perform a net‐
work transaction to satisfy statfs(2)
should not set this bit.
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_FMT_2TB_FILESIZE If this bit is set the volume format
supports file sizes larger than 4GB, and
potentially up to 2TB; it does not indi‐
cate whether the file system supports
files larger than that.
Introduced with Darwin 8.0 (Mac OS X
version 10.4).
VOL_CAP_FMT_OPENDENYMODES If this bit is set, the volume format
supports open deny modes (e.g., "open
for read write, deny write").
VOL_CAP_FMT_HIDDEN_FILES If this bit is set, the volume format
supports the UF_HIDDEN file flag, and
the UF_HIDDEN flag is mapped to that
volume's native "hidden" or "invisible"
bit (e.g., the invisible bit from the
Finder Info extended attribute).
VOL_CAP_FMT_PATH_FROM_ID If this bit is set, the volume format
supports the ability to derive a path‐
name to the root of the file system
given only the ID of an object. This
also implies that object IDs on this
file system are persistent and not recy‐
cled. Most file systems will not sup‐
port this capability.
VOL_CAP_FMT_NO_VOLUME_SIZES If this bit is set the volume format
does not support determining values for
total data blocks, available blocks, or
free blocks, as in f_blocks, f_bavail,
and f_bfree in the struct statfs
returned by statfs(2). Historically,
those values were set to 0xFFFFFFFF for
volumes that did not support them.
Introduced with Darwin 10.0 (Mac OS X
version 10.6).
VOL_CAP_FMT_64BIT_OBJECT_IDS If this bit is set, the volume format
uses object IDs that are 64-bit. This
means that ATTR_CMN_FILEID and
ATTR_CMN_PARENTID are the only legiti‐
mate attributes for obtaining object IDs
from this volume and the 32-bit
fid_objno fields of the fsobj_id_t
returned by ATTR_CMN_OBJID,
ATTR_CMN_OBJPERMANENTID, and
ATTR_CMN_PAROBJID are undefined.
The following bits are defined in the second element (indexed by
VOL_CAPABILITIES_INTERFACES) of the capabilities and valid fields of the
vol_capabilities_attr_t structure.
VOL_CAP_INT_SEARCHFS If this bit is set the volume format
implementation supports searchfs(2).
VOL_CAP_INT_ATTRLIST If this bit is set the volume format
implementation supports getattrlist()
and setattrlist(2).
VOL_CAP_INT_NFSEXPORT If this bit is set the volume format
implementation allows this volume to be
exported via NFS.
VOL_CAP_INT_READDIRATTR If this bit is set the volume format
implementation supports
getdirentriesattr(2).
VOL_CAP_INT_EXCHANGEDATA If this bit is set the volume format
implementation supports exchangedata(2).
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_INT_COPYFILE If this bit is set the volume format
implementation supports the (private and
undocumented) copyfile() function.
(This is not the copyfile(3) function.)
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_INT_ALLOCATE If this bit is set the volume format
implementation supports the
F_PREALLOCATE selector of fcntl(2).
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_INT_VOL_RENAME If this bit is set the volume format
implementation allows you to modify the
volume name using setattrlist(2).
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_INT_ADVLOCK If this bit is set the volume format
implementation supports advisory lock‐
ing, that is, the F_GETLK, F_SETLK, and
F_SETLKW selectors to fcntl(2).
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_INT_FLOCK If this bit is set the volume format
implementation supports whole file
locks. This includes flock(2) and the
O_EXLOCK and O_SHLOCK flags to open(2).
Introduced with Darwin 7.0 (Mac OS X
version 10.3).
VOL_CAP_INT_EXTENDED_SECURITY If this bit is set the volume format
implementation supports extended secu‐
rity controls (ACLs).
Introduced with Darwin 8.0 (Mac OS X
version 10.4).
VOL_CAP_INT_USERACCESS If this bit is set the volume format
implementation supports the
ATTR_CMN_USERACCESS attribute.
Introduced with Darwin 8.0 (Mac OS X
version 10.4).
VOL_CAP_INT_MANLOCK If this bit is set, the volume format
implementation supports AFP-style manda‐
tory byte range locks via ioctl(2).
VOL_CAP_INT_EXTENDED_ATTR If this bit is set, the volume format
implementation supports native extended
attributes (see setxattr(2) ).
VOL_CAP_INT_NAMEDSTREAMS If this bit is set, the volume format
implementation supports native named
streams.
A volume can also report which attributes it supports. This information
is returned by the ATTR_VOL_ATTRIBUTES attribute, which returns a
vol_attributes_attr_t structure (shown below).
typedef struct attribute_set {
attrgroup_t commonattr; /* common attribute group */
attrgroup_t volattr; /* volume attribute group */
attrgroup_t dirattr; /* directory attribute group */
attrgroup_t fileattr; /* file attribute group */
attrgroup_t forkattr; /* fork attribute group */
} attribute_set_t;
typedef struct vol_attributes_attr {
attribute_set_t validattr;
attribute_set_t nativeattr;
} vol_attributes_attr_t;
The validattr field consists of a number of bit sets that indicate
whether an attribute is supported by the volume format implementation.
The nativeattr is similar except that the bit sets indicate whether an
attribute is supported natively by the volume format. An attribute is
supported natively if the volume format implementation does not have to
do any complex conversions to access the attribute. For example, a vol‐
ume format might support persistent object identifiers, but doing so
requires a complex table lookup that is not part of the core volume for‐
mat. In that case, the ATTR_VOL_ATTRIBUTES attribute would return
ATTR_CMN_OBJPERMANENTID set in the validattr field of the
vol_attributes_attr_t, but not in the nativeattr field.
RETURN VALUES
Upon successful completion a value of 0 is returned. Otherwise, a value
of -1 is returned and errno is set to indicate the error.
COMPATIBILITY
Not all volumes support getattrlist(). The best way to test whether a
volume supports this function is to simply call it and check the error
result. getattrlist() will return ENOTSUP if it is not supported on a
particular volume.
The getattrlist() function has been undocumented for more than two years.
In that time a number of volume format implementations have been created
without a proper specification for the behaviour of this routine. You
may encounter volume format implementations with slightly different be‐
haviour than what is described here. Your program is expected to be tol‐
erant of this variant behaviour.
If you're implementing a volume format that supports getattrlist(), you
should be careful to support the behaviour specified by this document.
ERRORSgetattrlist() and fgetattrlist() will fail if:
[ENOTSUP] The volume does not support the query.
[ENOTDIR] A component of the path prefix for getattrlist() is
not a directory.
[ENAMETOOLONG] A component of a path name for getattrlist() exceeded
NAME_MAX characters, or an entire path name exceeded
PATH_MAX characters.
[ENOENT] The file system object for getattrlist() does not
exist.
[EBADF] The file descriptor argument for fgetattrlist() is not
a valid file descriptor.
[EACCES] Search permission is denied for a component of the
path prefix for getattrlist().
[ELOOP] Too many symbolic links were encountered in translat‐
ing the pathname for getattrlist().
[EFAULT] path, attrList or attrBuf points to an invalid
address.
[EINVAL] The bitmapcount field of attrList is not
ATTR_BIT_MAP_COUNT.
[EINVAL] You requested an invalid attribute.
[EINVAL] You requested an attribute that is not supported for
this file system object.
[EINVAL] You requested volume attributes and directory or file
attributes.
[EINVAL] You requested volume attributes but path does not ref‐
erence the root of the volume.
[EROFS] The volume is read-only but must be modified in order
to return this attribute.
[EIO] An I/O error occurred while reading from or writing to
the file system.
CAVEATS
If you request any volume attributes, you must set ATTR_VOL_INFO in the
volattr field, even though it generates no result in the attribute buf‐
fer.
The order that attributes are stored in the attribute buffer almost
invariably matches the order of attribute mask bit values. For example,
ATTR_CMN_NAME (0x00000001) comes before ATTR_CMN_DEVID (0x00000002)
because its value is smaller. However, you can not rely on this ordering
because there is one key exception: ATTR_CMN_FLAGS is placed after the
ATTR_CMN_NAMEDATTRCOUNT / ATTR_CMN_NAMEDATTRLIST pair, even though its
bit position indicates that it should come before. This is due to a bug
in an early version of Mac OS X that can't be fixed for binary compati‐
bility reasons. When ordering attributes, you should always use the
order in which they are described above.
The timespec structure is 64-bits (two 32-bit elements) in 32-bit code,
and 128-bits (two 64-bit elements) in 64-bit code; however, it is aligned
on a 4-byte (32-bit) boundary, even in 64-bit code.
If you use a structure for the attribute data, it must be correctly
packed and aligned (see examples).
Inconsistent behavior may be observed when the ATTR_CMN_FULLPATH
attribute is requested on hard-linked items, particularly when the file
system does not support ATTR_CMN_PARENTID natively. Callers should be
aware of this when requesting the full path of a hard-linked item, espe‐
cially if the full path crosses mount points.
For more caveats, see also the compatibility notes above.
EXAMPLES
The following code prints the file type and creator of a file, assuming
that the volume supports the required attributes.
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <sys/attr.h>
#include <sys/errno.h>
#include <unistd.h>
#include <sys/vnode.h>
typedef struct attrlist attrlist_t;
struct FInfoAttrBuf {
u_int32_t length;
fsobj_type_t objType;
char finderInfo[32];
} __attribute__((aligned(4), packed));
typedef struct FInfoAttrBuf FInfoAttrBuf;
static int FInfoDemo(const char *path)
{
int err;
attrlist_t attrList;
FInfoAttrBuf attrBuf;
memset(&attrList, 0, sizeof(attrList));
attrList.bitmapcount = ATTR_BIT_MAP_COUNT;
attrList.commonattr = ATTR_CMN_OBJTYPE | ATTR_CMN_FNDRINFO;
err = getattrlist(path, &attrList, &attrBuf, sizeof(attrBuf), 0);
if (err != 0) {
err = errno;
}
if (err == 0) {
assert(attrBuf.length == sizeof(attrBuf));
printf("Finder information for %s:\n", path);
switch (attrBuf.objType) {
case VREG:
printf("file type = '%.4s'\n", &attrBuf.finderInfo[0]);
printf("file creator = '%.4s'\n", &attrBuf.finderInfo[4]);
break;
case VDIR:
printf("directory\n");
break;
default:
printf("other object type, %d\n", attrBuf.objType);
break;
}
}
return err;
}
The following code is an alternative implementation that uses nested
structures to group the related attributes.
#include <assert.h>
#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <sys/attr.h>
#include <sys/errno.h>
#include <unistd.h>
#include <sys/vnode.h>
typedef struct attrlist attrlist_t;
struct FInfo2CommonAttrBuf {
fsobj_type_t objType;
char finderInfo[32];
} __attribute__((aligned(4), packed));
typedef struct FInfo2CommonAttrBuf FInfo2CommonAttrBuf;
struct FInfo2AttrBuf {
u_int32_t length;
FInfo2CommonAttrBuf common;
} __attribute__((aligned(4), packed));;
typedef struct FInfo2AttrBuf FInfo2AttrBuf;
static int FInfo2Demo(const char *path)
{
int err;
attrlist_t attrList;
FInfo2AttrBuf attrBuf;
memset(&attrList, 0, sizeof(attrList));
attrList.bitmapcount = ATTR_BIT_MAP_COUNT;
attrList.commonattr = ATTR_CMN_OBJTYPE | ATTR_CMN_FNDRINFO;
err = getattrlist(path, &attrList, &attrBuf, sizeof(attrBuf), 0);
if (err != 0) {
err = errno;
}
if (err == 0) {
assert(attrBuf.length == sizeof(attrBuf));
printf("Finder information for %s:\n", path);
switch (attrBuf.common.objType) {
case VREG:
printf(
"file type = '%.4s'\n",
&attrBuf.common.finderInfo[0]
);
printf(
"file creator = '%.4s'\n",
&attrBuf.common.finderInfo[4]
);
break;
case VDIR:
printf("directory\n");
break;
default:
printf(
"other object type, %d\n",
attrBuf.common.objType
);
break;
}
}
return err;
}
The following example shows how to deal with variable length attributes.
It assumes that the volume specified by path supports the necessary
attributes.
#include <assert.h>
#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <sys/attr.h>
#include <sys/errno.h>
#include <unistd.h>
#include <sys/vnode.h>
typedef struct attrlist attrlist_t;
struct VolAttrBuf {
u_int32_t length;
u_int32_t fileCount;
u_int32_t dirCount;
attrreference_t mountPointRef;
attrreference_t volNameRef;
char mountPointSpace[MAXPATHLEN];
char volNameSpace[MAXPATHLEN];
} __attribute__((aligned(4), packed));
typedef struct VolAttrBuf VolAttrBuf;
static int VolDemo(const char *path)
{
int err;
attrlist_t attrList;
VolAttrBuf attrBuf;
memset(&attrList, 0, sizeof(attrList));
attrList.bitmapcount = ATTR_BIT_MAP_COUNT;
attrList.volattr = ATTR_VOL_INFO
| ATTR_VOL_FILECOUNT
| ATTR_VOL_DIRCOUNT
| ATTR_VOL_MOUNTPOINT
| ATTR_VOL_NAME;
err = getattrlist(path, &attrList, &attrBuf, sizeof(attrBuf), 0);
if (err != 0) {
err = errno;
}
if (err == 0) {
assert(attrBuf.length > offsetof(VolAttrBuf, mountPointSpace));
assert(attrBuf.length <= sizeof(attrBuf));
printf("Volume information for %s:\n", path);
printf("ATTR_VOL_FILECOUNT: %u\n", attrBuf.fileCount);
printf("ATTR_VOL_DIRCOUNT: %u\n", attrBuf.dirCount);
printf(
"ATTR_VOL_MOUNTPOINT: %.*s\n",
(int) attrBuf.mountPointRef.attr_length,
( ((char *) &attrBuf.mountPointRef)
+ attrBuf.mountPointRef.attr_dataoffset )
);
printf(
"ATTR_VOL_NAME: %.*s\n",
(int) attrBuf.volNameRef.attr_length,
( ((char *) &attrBuf.volNameRef)
+ attrBuf.volNameRef.attr_dataoffset )
);
}
return err;
}
The following sample demonstrates the need to use packing and alignment
controls; without the attribute, in 64-bit code, the fields of the struc‐
ture are not placed at the locations that the kernel expects.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <err.h>
#include <time.h>
#include <sys/attr.h>
/* The alignment and packing attribute is necessary in 64-bit code */
struct AttrListTimes {
u_int32_t length;
struct timespec st_crtime;
struct timespec st_modtime;
} __attribute__((aligned(4), packed));
main(int argc, char **argv)
{
int rv;
int i;
for (i = 1; i < argc; i++) {
struct attrlist attrList;
struct AttrListTimes myStat = {0};
char *path = argv[i];
memset(&attrList, 0, sizeof(attrList));
attrList.bitmapcount = ATTR_BIT_MAP_COUNT;
attrList.commonattr = ATTR_CMN_CRTIME |
ATTR_CMN_MODTIME;
rv = getattrlist(path, &attrList, &myStat, sizeof(myStat), 0);
if (rv == -1) {
warn("getattrlist(%s)", path);
continue;
}
printf("%s: Modification time = %s", argv[i], ctime(&myStat.st_modtime.tv_sec));
}
return 0;
}
SEE ALSOaccess(2), chflags(2), exchangedata(2), fcntl(2), getdirentriesattr(2),
mount(2), searchfs(2), setattrlist(2), stat(2), statfs(2)HISTORY
A getattrlist() function call appeared in Darwin 1.3.1 (Mac OS X version
10.0).
Darwin October 14, 2004 Darwin
