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open(2): Add O_DSYNC flag.

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POSIX O_DSYNC means that writes include an implicit fdatasync(2), just
as O_SYNC implies fsync(2).

VOP_WRITE() functions that understand the new IO_DATASYNC flag can act
accordingly, but we'll still pass down IO_SYNC so that file systems that
don't understand it will continue to provide the stronger O_SYNC
behaviour.

Flag also applies to fcntl(2).

Reviewed by: kib, delphij
Differential Revision: https://reviews.freebsd.org/D25090
This commit is contained in:
Thomas Munro 2021-01-07 23:46:51 +13:00
parent 81098ca81d
commit a5e284038e
7 changed files with 49 additions and 16 deletions
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19
lib/libc/sys/fcntl.2
View File

@ -28,7 +28,7 @@
.\" @(#)fcntl.2 8.2 (Berkeley) 1/12/94
.\" $FreeBSD$
.\"
.Dd January 17, 2020
.Dd January 6, 2021
.Dt FCNTL 2
.Os
.Sh NAME
@ -196,7 +196,7 @@ The flags for the
.Dv F_GETFL
and
.Dv F_SETFL
flags are as follows:
commands are as follows:
.Bl -tag -width O_NONBLOCKX
.It Dv O_NONBLOCK
Non-blocking I/O; if no data is available to a
@ -225,6 +225,21 @@ Enable the
signal to be sent to the process group
when I/O is possible, e.g.,
upon availability of data to be read.
.It Dv O_SYNC
Enable synchronous writes.
Corresponds to the
.Dv O_SYNC
flag of
.Xr open 2 .
.Dv O_FSYNC
is an historical synonym for
.Dv O_SYNC .
.It Dv O_DSYNC
Enable synchronous data writes.
Corresponds to the
.Dv O_DSYNC
flag of
.Xr open 2 .
.El
.Pp
The seals that may be applied with

20
lib/libc/sys/open.2
View File

@ -181,8 +181,9 @@ O_EXCL error if create and file exists
O_SHLOCK atomically obtain a shared lock
O_EXLOCK atomically obtain an exclusive lock
O_DIRECT eliminate or reduce cache effects
O_FSYNC synchronous writes
O_FSYNC synchronous writes (historical synonym for O_SYNC)
O_SYNC synchronous writes
O_DSYNC synchronous data writes
O_NOFOLLOW do not follow symlinks
O_NOCTTY ignored
O_TTY_INIT ignored
@ -230,15 +231,18 @@ returns immediately.
The descriptor remains in non-blocking mode for subsequent operations.
.Pp
If
.Dv O_FSYNC
.Dv O_SYNC
is used in the mask, all writes will
immediately and synchronously be written to disk.
.Pp
.Dv O_SYNC
is a synonym for
.Dv O_FSYNC
required by
.Tn POSIX .
is an historical synonym for
.Dv O_SYNC .
.Pp
If
.Dv O_DSYNC
is used in the mask, all data and metadata required to read the data will be
synchronously written to disk, but changes to metadata such as file access and
modification timestamps may be written later.
.Pp
If
.Dv O_NOFOLLOW
@ -651,6 +655,8 @@ The
.Fn openat
function was introduced in
.Fx 8.0 .
.Dv O_DSYNC
appeared in 13.0.
.Sh BUGS
The Open Group Extended API Set 2 specification requires that the test
for whether

1
sys/contrib/openzfs/include/os/freebsd/spl/sys/ccompile.h
View File

@ -168,7 +168,6 @@ extern "C" {
#define O_LARGEFILE 0
#define O_RSYNC 0
#define O_DSYNC 0
#ifndef LOCORE
#ifndef HAVE_RPC_TYPES

2
sys/contrib/openzfs/include/os/freebsd/spl/sys/vnode.h
View File

@ -127,7 +127,9 @@ vn_is_readonly(vnode_t *vp)
#define FCREAT O_CREAT
#define FTRUNC O_TRUNC
#define FEXCL O_EXCL
#ifndef FDSYNC
#define FDSYNC FFSYNC
#endif
#define FRSYNC FFSYNC
#define FSYNC FFSYNC
#define FOFFMAX 0x00

7
sys/kern/vfs_vnops.c
View File

@ -1066,6 +1066,13 @@ vn_write(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags,
if ((fp->f_flag & O_FSYNC) ||
(vp->v_mount && (vp->v_mount->mnt_flag & MNT_SYNCHRONOUS)))
ioflag |= IO_SYNC;
/*
* For O_DSYNC we set both IO_SYNC and IO_DATASYNC, so that VOP_WRITE()
* implementations that don't understand IO_DATASYNC fall back to full
* O_SYNC behavior.
*/
if (fp->f_flag & O_DSYNC)
ioflag |= IO_SYNC | IO_DATASYNC;
mp = NULL;
if (vp->v_type != VCHR &&
(error = vn_start_write(vp, &mp, V_WAIT | PCATCH)) != 0)

15
sys/sys/fcntl.h
View File

@ -141,8 +141,10 @@ typedef __pid_t pid_t;
return back */
#endif
#define O_DSYNC 0x00800000 /* POSIX data sync */
/*
* XXX missing O_DSYNC, O_RSYNC.
* XXX missing O_RSYNC.
*/
#ifdef _KERNEL
@ -158,9 +160,9 @@ typedef __pid_t pid_t;
#define OFLAGS(fflags) ((fflags) & O_EXEC ? (fflags) : (fflags) - 1)
/* bits to save after open */
#define FMASK (FREAD|FWRITE|FAPPEND|FASYNC|FFSYNC|FNONBLOCK|O_DIRECT|FEXEC)
#define FMASK (FREAD|FWRITE|FAPPEND|FASYNC|FFSYNC|FDSYNC|FNONBLOCK|O_DIRECT|FEXEC)
/* bits settable by fcntl(F_SETFL, ...) */
#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK|FRDAHEAD|O_DIRECT)
#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FDSYNC|FNONBLOCK|FRDAHEAD|O_DIRECT)
#if defined(COMPAT_FREEBSD7) || defined(COMPAT_FREEBSD6) || \
defined(COMPAT_FREEBSD5) || defined(COMPAT_FREEBSD4)
@ -185,15 +187,16 @@ typedef __pid_t pid_t;
#define FAPPEND O_APPEND /* kernel/compat */
#define FASYNC O_ASYNC /* kernel/compat */
#define FFSYNC O_FSYNC /* kernel */
#define FDSYNC O_DSYNC /* kernel */
#define FNONBLOCK O_NONBLOCK /* kernel */
#define FNDELAY O_NONBLOCK /* compat */
#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
* Historically, we ran out of bits in f_flag (which was once a short).
* However, the flag bits not set in FMASK are only meaningful in the
* initial open syscall. Those bits were thus given a
* different meaning for fcntl(2).
*/
#if __BSD_VISIBLE

1
sys/sys/vnode.h
View File

@ -326,6 +326,7 @@ struct vattr {
#define IO_NOMACCHECK 0x1000 /* MAC checks unnecessary */
#define IO_BUFLOCKED 0x2000 /* ffs flag; indir buf is locked */
#define IO_RANGELOCKED 0x4000 /* range locked */
#define IO_DATASYNC 0x8000 /* do only data I/O synchronously */
#define IO_SEQMAX 0x7F /* seq heuristic max value */
#define IO_SEQSHIFT 16 /* seq heuristic in upper 16 bits */