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Submit #2356 » 0001-Add-O_CLOEXEC-flag-to-open-2-and-fhopen-2.patch

ftigeot, 07/29/2012 11:28 AM

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lib/libc/sys/open.2
.\" SUCH DAMAGE.
.\"
.\" @(#)open.2 8.2 (Berkeley) 11/16/93
.\" $FreeBSD: src/lib/libc/sys/open.2,v 1.11.2.9 2001/12/14 18:34:01 ru Exp $
.\" $DragonFly: src/lib/libc/sys/open.2,v 1.3 2005/07/29 23:16:04 hsu Exp $
.\" $FreeBSD: src/lib/libc/sys/open.2,v 1.43 2011/03/25 14:01:18 kib Exp $
.\"
.Dd July 24, 2009
.Dd March 25, 2011
.Dt OPEN 2
.Os
.Sh NAME
......
O_DIRECT eliminate or reduce cache effects
O_FSYNC synchronous writes
O_NOFOLLOW do not follow symlinks
O_CLOEXEC set FD_CLOEXEC upon open
.Ed
.Pp
Opening a file with
......
it will minimize the impact the data has on the cache.
Use of this flag can drastically reduce performance if not used with care.
.Pp
.Dv O_CLOEXEC
may be used to set
.Dv FD_CLOEXEC
flag for the newly returned file descriptor.
.Pp
If successful,
.Fn open
and
......
When a new file is created it is given the group of the directory
which contains it.
.Pp
The new descriptor is set to remain open across
Unless
.Dv
O_CLOEXEC
flag was specified,
the new descriptor is set to remain open across
.Xr execve 2
system calls; see
.Xr close 2
.Xr close 2 ,
.Xr fcntl 2
and
.Xr fcntl 2 .
.Dv O_CLOEXEC
description.
.Pp
The system imposes a limit on the number of file descriptors
open simultaneously by one process.
sys/kern/kern_descrip.c
* MPSAFE
*/
int
falloc(struct lwp *lp, struct file **resultfp, int *resultfd)
fallocf(struct lwp *lp, struct file **resultfp, int *resultfd, int flags)
{
static struct timeval lastfail;
static int curfail;
......
fp->f_ops = &badfileops;
fp->f_seqcount = 1;
fsetcred(fp, cred);
if ((flags & O_CLOEXEC) != 0)
fp->f_flag |= UF_EXCLOSE;
spin_lock(&filehead_spin);
nfiles++;
LIST_INSERT_HEAD(&filehead, fp, f_list);
......
return (error);
}
int
falloc(struct lwp *lp, struct file **resultfp, int *resultfd)
{
return fallocf(lp, resultfp, resultfd, 0);
}
/*
* Check for races against a file descriptor by determining that the
* file pointer is still associated with the specified file descriptor,
sys/kern/vfs_syscalls.c
if ((oflags & O_ACCMODE) == O_ACCMODE)
return (EINVAL);
flags = FFLAGS(oflags);
error = falloc(lp, &nfp, NULL);
error = fallocf(lp, &nfp, NULL, flags);
if (error)
return (error);
fp = nfp;
......
* WARNING! no f_nchandle will be associated when fhopen()ing a
* directory. XXX
*/
if ((error = falloc(td->td_lwp, &nfp, &indx)) != 0)
if ((error = fallocf(td->td_lwp, &nfp, &indx, fmode)) != 0)
goto bad;
fp = nfp;
sys/sys/fcntl.h
/* Attempt to bypass the buffer cache */
#define O_DIRECT 0x00010000
#define O_CLOEXEC 0x00020000 /* atomically set FD_CLOEXEC */
#define O_FBLOCKING 0x00040000 /* force blocking I/O */
#define O_FNONBLOCKING 0x00080000 /* force non-blocking I/O */
#define O_FAPPEND 0x00100000 /* force append mode for write */
sys/sys/filedesc.h
int dupfdopen (struct filedesc *, int, int, int, int);
int fdalloc (struct proc *p, int want, int *result);
int fdavail (struct proc *p, int n);
int fallocf(struct lwp *lp, struct file **resultfp, int *resultfd, int flags);
int falloc (struct lwp *lp, struct file **resultfp, int *resultfd);
void fsetfd (struct filedesc *fdp, struct file *fp, int fd);
int fgetfdflags(struct filedesc *fdp, int fd, int *flagsp);
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