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Implement POSIX.1b shared memory objects. In this implementation,

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shared memory objects are regular files; the shm_open(3) routine
uses fcntl(2) to set a flag on the descriptor which tells mmap(2)
to automatically apply MAP_NOSYNC.

Not objected to by: bde, dillon, dufault, jasone
This commit is contained in:
Garrett Wollman 2000-04-22 15:22:31 +00:00
parent b39b38ecd0
commit aa543039b5
3 changed files with 32 additions and 2 deletions
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20
sys/sys/fcntl.h
View File

@ -106,12 +106,12 @@
/* bits to save after open */
#define FMASK (FREAD|FWRITE|FAPPEND|FASYNC|FFSYNC|FNONBLOCK)
/* bits settable by fcntl(F_SETFL, ...) */
#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK)
#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK|FPOSIXSHM)
#endif
/*
* The O_* flags used to have only F* names, which were used in the kernel
* and by fcntl. We retain the F* names for the kernel f_flags field
* and by fcntl. We retain the F* names for the kernel f_flag field
* and for backward compatibility for fcntl.
*/
#ifndef _POSIX_SOURCE
@ -123,6 +123,22 @@
#define O_NDELAY O_NONBLOCK /* compat */
#endif
/*
* We are out of bits in f_flag (which is a short). However,
* the flag bits not set in FMASK are only meaningful in the
* initial open syscall. Those bits can thus be given a
* different meaning for fcntl(2).
*/
#ifndef _POSIX_SOURCE
/*
* Set by shm_open(3) to get automatic MAP_ASYNC behavior
* for POSIX shared memory objects (which are otherwise
* implemented as plain files).
*/
#define FPOSIXSHM O_NOFOLLOW
#endif
/*
* Constants used for fcntl(2)
*/

4
sys/sys/unistd.h
View File

@ -160,6 +160,10 @@
#define _POSIX_MEMLOCK_RANGE
#endif
/* ??? #define _POSIX_FSYNC 1 */
#define _POSIX_MAPPED_FILES 1
#define _POSIX_SHARED_MEMORY_OBJECTS 1
/* POSIX.1B sysconf options */
#define _SC_ASYNCHRONOUS_IO 28
#define _SC_MAPPED_FILES 29

10
sys/vm/vm_mmap.c
View File

@ -282,6 +282,16 @@ mmap(p, uap)
return (EBADF);
if (fp->f_type != DTYPE_VNODE)
return (EINVAL);
/*
* POSIX shared-memory objects are defined to have
* kernel persistence, and are not defined to support
* read(2)/write(2) -- or even open(2). Thus, we can
* use MAP_ASYNC to trade on-disk coherence for speed.
* The shm_open(3) library routine turns on the FPOSIXSHM
* flag to request this behavior.
*/
if (fp->f_flag & FPOSIXSHM)
flags |= MAP_NOSYNC;
vp = (struct vnode *) fp->f_data;
if (vp->v_type != VREG && vp->v_type != VCHR)
return (EINVAL);