svcadm(1M)을 검색하려면 섹션에서 1M 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
shmop(2)
shmop(2) System Calls shmop(2)
NAME
shmop, shmat, shmdt - shared memory operations
SYNOPSIS
#include <sys/types.h>
#include <sys/shm.h>
void *shmat(int shmid, const void *shmaddr, int shmflg);
int shmdt(const void *shmaddr);
DESCRIPTION
The shmat() function attaches the shared memory segment associated with
the shared memory identifier specified by shmid to the data segment of
the calling process.
The permission required for a shared memory control operation is given
as {token}, where token is the type of permission needed. The types of
permission are interpreted as follows:
00400 READ by user
00200 WRITE by user
00040 READ by group
00020 WRITE by group
00004 READ by others
00002 WRITE by others
See the Shared Memory Operation Permissions section of Intro(2) for
more information.
For shared memory segments created with the SHM_SHARE_MMU or SHM_PAGE‐
ABLE flags, the default protections cannot be changed so as to prevent
a single process from affecting other processes sharing the same shared
segment.
When (shmflg & SHM_SHARE_MMU) is true, virtual memory resources in
addition to shared memory itself are shared among processes that use
the same shared memory.
When (shmflg & SHM_PAGEABLE) is true, virtual memory resources are
shared and the dynamic shared memory (DISM) framework is created. The
dynamic shared memory can be resized dynamically within the specified
size in shmget(2). The DISM shared memory is pageable unless it is
locked.
Segments created using shmget_osm(2) may not be attached with shmflag
flags of SHM_SHARE_MMU, SHM_PAGEABLE, or SHM_RND.
The shared memory segment is attached to the data segment of the call‐
ing process at the address specified based on one of the following cri‐
teria:
o If shmaddr is equal to NULL, the segment is attached to the
first available address as selected by the system.
o If shmaddr is equal to NULL and (shmflg & SHM_SHARE_MMU) or
(shmflg & SHM_PAGEABLE) is true, then the segment is
attached to the first available suitably aligned address.
When (shmflg & SHM_SHARE_MMU) or (shmflg & SHM_PAGEABLE)
is set, however, the permission given by shmget() determines
whether the segment is attached for reading or reading and
writing.
o If shmaddr is not equal to NULL and (shmflg & SHM_RND) is
true, the segment is attached to the address given by
(shmaddr − (shmaddr modulus SHMLBA)).
o If shmaddr is not equal to NULL and (shmflg & SHM_RND) is
false, the segment is attached to the address given by
shmaddr.
o The segment is attached for reading if (shmflg &
SHM_RDONLY) is true {READ}, otherwise it is attached for
reading and writing {READ/WRITE}.
The shmdt() function detaches from the calling process's data segment
the shared memory segment located at the address specified by shmaddr.
Shared memory segments must be explicitly removed after the last refer‐
ence to them has been removed.
Upon successful completion, shmat() increments the value of shm_nattch
and updates the shm_atime timestamp in the shmid_ds structure associ‐
ated with the shared memory segment; shmdt() decrements the value of
shm_nattch and updates the shm_dtime timestamp. See the Shared Memory
Identifier section of Intro(2) for more information.
RETURN VALUES
Upon successful completion, shmat() returns the data segment start
address of the attached shared memory segment. Otherwise, SHM_FAILED
(−1) is returned, the shared memory segment is not attached, and errno
is set to indicate the error.
Upon successful completion, shmdt() returns 0. Otherwise, SHM_FAILED
(−1) is returned, the shared memory segment is not detached, and errno
is set to indicate the error.
ERRORS
The shmat() function will fail if:
EACCES Operation permission is denied to the calling process (see
Intro(2)).
EINVAL The shmid argument is not a valid shared memory identifier.
The shmaddr argument is not equal to 0, and the value of
(shmaddr − (shmaddr modulus SHMLBA)) is an illegal address.
The shmaddr argument is not equal to 0, is an illegal
address, and (shmflg & SHM_RND) is false.
The shmaddr argument is not equal to 0, is not properly
aligned, and (shmflg & SHM_SHARE_MMU) is true.
SHM_SHARE_MMU is not supported in certain architectures.
Both (shmflg & SHM_SHARE_MMU) and (shmflg & SHM_PAGEABLE)
are true.
(shmflg & SHM_SHARE_MMU) is true and the shared memory seg‐
ment specified by shmid() had previously been attached by a
call to shmat() in which (shmflg & SHM_PAGEABLE) was true.
(shmflg & SHM_PAGEABLE) is true and the shared memory seg‐
ment specified by shmid() had previously been attached by a
call to shmat() in which (shmflg & SHM_SHARE_MMU) was true.
The segment was created using shmget_osm(2), and one of (shm‐
flg & SHM_PAGEABLE), (shmflg & SHM_SHARE_MMU), or (shmflg
& SHM_RND) is true.
The segment was created using shmget_osm(2), and the shmaddr
argument is not equal to 0, and shmaddr is not aligned to the
segment's granule size.
EMFILE The number of shared memory segments attached to the calling
process would exceed the system-imposed limit.
ENOMEM The available data space is not large enough to accommodate
the shared memory segment.
The shmdt() function will fail if:
EINVAL The shmaddr argument is not the data segment start address of
a shared memory segment.
ENOMEM (shmflg & SHM_SHARE_MMU) is true and attaching to the shared
memory segment would exceed a limit or resource control on
locked memory.
WARNINGS
Using a fixed value for the shmaddr argument can adversely affect per‐
formance on certain platforms due to D-cache aliasing.
Using a fixed value for the shmaddr argument can also result in hard-
to-reproduce failures to attach shared memory segments at a given
address when Address Space Layout Randomization (ASLR) is enabled. Pro‐
grams that require specifying memory layouts can be tagged at link time
to disable ASLR for their process. For more information, see the ld(1)
and sxadm(8) man pages.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelAsync-Signal-
Safe _ StandardSee standards(7).
SEE ALSO
exec(2), exit(2), fork(2), Intro(2), shmctl(2), shmget(2),
shmget_osm(2), attributes(7), standards(7)
HISTORY
The shmat() and shmdt() functions, and the flags SHM_RDONLY and
SHM_RND, have been included in all Sun and Oracle releases of Solaris
since Solaris 2.0.
Support for the SHM_SHARE_MMU flag was added to Solaris in the Solaris
2.2 release.
Support for the SHM_PAGEABLE flag was added to Solaris in the Solaris 8
1/01 (Update 3) release.
Oracle Solaris 11.4 15 Sep 2020 shmop(2)