SDGET(S) XENIX System V SDGET(S)
Name
sdget, sdfree - Attaches and detaches a shared data segment.
Syntax
#include <sys/sd.h>
char *sdget(path, flags, size, [mode])
char *path;
int flags, mode;
long size;
int sdfree(addr);
char *addr;
Description
sdget attaches a shared data segment to the data space of
the current process. The actions performed are controlled
by the value of flags. flags values are constructed by OR-
ing flags from the following list:
SD_RDONLY Attach the segment for reading only.
SD_WRITE Attach the segment for both reading and writing.
SD_CREAT If the segment named by path exists and is not
in use (active), this flag will have the same
effect as creating a segment from scratch.
Otherwise, the segment is created according to
the values of size and mode. Read and write
access to the segment is granted to other
processes based on the permissions passed in
mode, and functions the same as those for
regular files. Execute permission is
meaningless. The segment is initialized to
contain all zeroes.
SD_UNLOCK If the segment is created because of this call,
the segment will be made so that more than one
process can be between sdenter and sdleave
calls.
sdfree detaches the current process from the shared data
segment that is attached at the specified address. If the
current process has done sdenter but not an sdleave for the
specified segment, sdleave will be done before detaching the
segment.
When no process remains attached to the segment, the
contents of that segment disappear, and no process can
attach to the segment without creating it by using the
SD_CREAT flag in sdget. errno is set to EEXIST if a process
tries to create a shared data segment that exists and is in
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SDGET(S) XENIX System V SDGET(S)
use. errno is set to ENOTNAM if a process attempts an sdget
on a file that exists but is not a shared data type.
Notes
Use of the SD_UNLOCK flag on systems without hardware
support for shared data may cause severe performance
degradation.
For 286 programs, it is strongly recommended that sdget and
other shared data functions be reserved for large model
programs only. Small or middle model programs that attempt
to use shared data may run out of available memory. Also,
due to the 286 hardware, it is not possible to enforce the
read-only aspect of small model shared data. However,
read-only segments are honored in large model programs.
The 386 provides a 32 bit address space, even in small
model. As a result, shared data may be conveniently used
without regard to the restrictions that apply to 286
programs.
sdget automatically increments the process's original break
value to the memory location immediately after the shared
data segment. This affects subsequent sbrk or brk calls
which attempt to restore the original break value. In
particular, attempts to restore the break value to its value
before the sdget call causes an error.
This feature is a XENIX specific enhancement and may not be
present in all UNIX implementations. This routine must be
linked using the linker option -lx.
Return Value
On successful completion, the address at which the segment
was attached is returned. Otherwise, -1 is returned, and
errno is set to indicate the error. errno is set to EINVAL
if a process does an sdget on a shared data segment to which
it is already attached. errno is set to EEXIST if a process
tries to create a shared data segment that exists and is in
use. errno is set to ENOTNAM if a process attempts an sdget
on a file that exists but is not a shared data type.
The mode parameter must be included on the first call of the
sdget() function.
See Also
sdenter(S), sdgetv(S), sbrk(S)
Notes
The size variable in sdget has changed from unsigned to long
between Version 3.0 and System V. Although this requires
that source code be modified to use a long size parameter
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SDGET(S) XENIX System V SDGET(S)
when compiling with the System V libraries, an unsigned size
parameter will still be correctly interpreted by the kernel
when passed by binaries compiled with the Version 3.0
libraries.
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