Datasets:
memorylost731
/
linux_man_pages_library

Dataset card Data Studio Files Community
1
text
stringlengths
0
234
.b o_rdonly
open the object for read access.
a shared memory object opened in this way can be
.br mmap (2)ed
only for read
.rb ( prot_read )
access.
.tp
.b o_rdwr
open the object for read-write access.
.tp
.b o_creat
create the shared memory object if it does not exist.
the user and group ownership of the object are taken
from the corresponding effective ids of the calling process,
.\" in truth it is actually the filesystem ids on linux, but these
.\" are nearly always the same as the effective ids. (mtk, jul 05)
and the object's
permission bits are set according to the low-order 9 bits of
.ir mode ,
except that those bits set in the process file mode
creation mask (see
.br umask (2))
are cleared for the new object.
a set of macro constants which can be used to define
.i mode
is listed in
.br open (2).
(symbolic definitions of these constants can be obtained by including
.ir <sys/stat.h> .)
.ip
a new shared memory object initially has zero length\(emthe size of the
object can be set using
.br ftruncate (2).
the newly allocated bytes of a shared memory
object are automatically initialized to 0.
.tp
.b o_excl
if
.b o_creat
was also specified, and a shared memory object with the given
.i name
already exists, return an error.
the check for the existence of the object, and its creation if it
does not exist, are performed atomically.
.tp
.b o_trunc
if the shared memory object already exists, truncate it to zero bytes.
.pp
definitions of these flag values can be obtained by including
.ir <fcntl.h> .
.pp
on successful completion
.br shm_open ()
returns a new file descriptor referring to the shared memory object.
this file descriptor is guaranteed to be the lowest-numbered file descriptor
not previously opened within the process.
the
.b fd_cloexec
flag (see
.br fcntl (2))
is set for the file descriptor.
.pp
the file descriptor is normally used in subsequent calls
to
.br ftruncate (2)
(for a newly created object) and
.br mmap (2).
after a call to
.br mmap (2)
the file descriptor may be closed without affecting the memory mapping.
.pp
the operation
of
.br shm_unlink ()
is analogous to
.br unlink (2):
it removes a shared memory object name, and, once all processes
have unmapped the object, deallocates and
destroys the contents of the associated memory region.
after a successful
.br shm_unlink (),
attempts to
.br shm_open ()
an object with the same
.i name
fail (unless
.b o_creat
was specified, in which case a new, distinct object is created).
.sh return value
on success,
.br shm_open ()
returns a file descriptor (a nonnegative integer).
on success,
.br shm_unlink ()
returns 0.
on failure, both functions return \-1 and set
.i errno
to indicate the error.
.sh errors