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open(2): Add O_DSYNC flag.
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
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@ -28,7 +28,7 @@
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.\" @(#)fcntl.2 8.2 (Berkeley) 1/12/94
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.\" $FreeBSD$
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.\"
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.Dd January 17, 2020
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.Dd January 6, 2021
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.Dt FCNTL 2
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.Os
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.Sh NAME
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@ -196,7 +196,7 @@ The flags for the
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.Dv F_GETFL
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and
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.Dv F_SETFL
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flags are as follows:
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commands are as follows:
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.Bl -tag -width O_NONBLOCKX
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.It Dv O_NONBLOCK
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Non-blocking I/O; if no data is available to a
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@ -225,6 +225,21 @@ Enable the
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signal to be sent to the process group
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when I/O is possible, e.g.,
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upon availability of data to be read.
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.It Dv O_SYNC
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Enable synchronous writes.
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Corresponds to the
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.Dv O_SYNC
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flag of
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.Xr open 2 .
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.Dv O_FSYNC
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is an historical synonym for
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.Dv O_SYNC .
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.It Dv O_DSYNC
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Enable synchronous data writes.
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Corresponds to the
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.Dv O_DSYNC
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flag of
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.Xr open 2 .
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.El
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.Pp
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The seals that may be applied with
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@ -181,8 +181,9 @@ O_EXCL error if create and file exists
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O_SHLOCK atomically obtain a shared lock
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O_EXLOCK atomically obtain an exclusive lock
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O_DIRECT eliminate or reduce cache effects
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O_FSYNC synchronous writes
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O_FSYNC synchronous writes (historical synonym for O_SYNC)
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O_SYNC synchronous writes
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O_DSYNC synchronous data writes
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O_NOFOLLOW do not follow symlinks
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O_NOCTTY ignored
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O_TTY_INIT ignored
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@ -230,15 +231,18 @@ returns immediately.
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The descriptor remains in non-blocking mode for subsequent operations.
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.Pp
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If
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.Dv O_FSYNC
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.Dv O_SYNC
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is used in the mask, all writes will
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immediately and synchronously be written to disk.
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.Pp
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.Dv O_SYNC
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is a synonym for
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.Dv O_FSYNC
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required by
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.Tn POSIX .
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is an historical synonym for
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.Dv O_SYNC .
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.Pp
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If
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.Dv O_DSYNC
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is used in the mask, all data and metadata required to read the data will be
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synchronously written to disk, but changes to metadata such as file access and
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modification timestamps may be written later.
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.Pp
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If
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.Dv O_NOFOLLOW
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@ -651,6 +655,8 @@ The
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.Fn openat
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function was introduced in
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.Fx 8.0 .
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.Dv O_DSYNC
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appeared in 13.0.
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.Sh BUGS
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The Open Group Extended API Set 2 specification requires that the test
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for whether
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@ -168,7 +168,6 @@ extern "C" {
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#define O_LARGEFILE 0
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#define O_RSYNC 0
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#define O_DSYNC 0
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#ifndef LOCORE
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#ifndef HAVE_RPC_TYPES
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@ -127,7 +127,9 @@ vn_is_readonly(vnode_t *vp)
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#define FCREAT O_CREAT
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#define FTRUNC O_TRUNC
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#define FEXCL O_EXCL
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#ifndef FDSYNC
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#define FDSYNC FFSYNC
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#endif
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#define FRSYNC FFSYNC
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#define FSYNC FFSYNC
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#define FOFFMAX 0x00
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@ -1066,6 +1066,13 @@ vn_write(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags,
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if ((fp->f_flag & O_FSYNC) ||
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(vp->v_mount && (vp->v_mount->mnt_flag & MNT_SYNCHRONOUS)))
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ioflag |= IO_SYNC;
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/*
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* For O_DSYNC we set both IO_SYNC and IO_DATASYNC, so that VOP_WRITE()
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* implementations that don't understand IO_DATASYNC fall back to full
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* O_SYNC behavior.
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*/
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if (fp->f_flag & O_DSYNC)
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ioflag |= IO_SYNC | IO_DATASYNC;
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mp = NULL;
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if (vp->v_type != VCHR &&
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(error = vn_start_write(vp, &mp, V_WAIT | PCATCH)) != 0)
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@ -141,8 +141,10 @@ typedef __pid_t pid_t;
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return back */
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#endif
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#define O_DSYNC 0x00800000 /* POSIX data sync */
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/*
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* XXX missing O_DSYNC, O_RSYNC.
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* XXX missing O_RSYNC.
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*/
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#ifdef _KERNEL
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@ -158,9 +160,9 @@ typedef __pid_t pid_t;
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#define OFLAGS(fflags) ((fflags) & O_EXEC ? (fflags) : (fflags) - 1)
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/* bits to save after open */
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#define FMASK (FREAD|FWRITE|FAPPEND|FASYNC|FFSYNC|FNONBLOCK|O_DIRECT|FEXEC)
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#define FMASK (FREAD|FWRITE|FAPPEND|FASYNC|FFSYNC|FDSYNC|FNONBLOCK|O_DIRECT|FEXEC)
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/* bits settable by fcntl(F_SETFL, ...) */
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#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK|FRDAHEAD|O_DIRECT)
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#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FDSYNC|FNONBLOCK|FRDAHEAD|O_DIRECT)
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#if defined(COMPAT_FREEBSD7) || defined(COMPAT_FREEBSD6) || \
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defined(COMPAT_FREEBSD5) || defined(COMPAT_FREEBSD4)
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#define FAPPEND O_APPEND /* kernel/compat */
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#define FASYNC O_ASYNC /* kernel/compat */
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#define FFSYNC O_FSYNC /* kernel */
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#define FDSYNC O_DSYNC /* kernel */
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#define FNONBLOCK O_NONBLOCK /* kernel */
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#define FNDELAY O_NONBLOCK /* compat */
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#define O_NDELAY O_NONBLOCK /* compat */
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#endif
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/*
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* We are out of bits in f_flag (which is a short). However,
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* the flag bits not set in FMASK are only meaningful in the
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* initial open syscall. Those bits can thus be given a
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* Historically, we ran out of bits in f_flag (which was once a short).
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* However, the flag bits not set in FMASK are only meaningful in the
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* initial open syscall. Those bits were thus given a
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* different meaning for fcntl(2).
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*/
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#if __BSD_VISIBLE
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@ -326,6 +326,7 @@ struct vattr {
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#define IO_NOMACCHECK 0x1000 /* MAC checks unnecessary */
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#define IO_BUFLOCKED 0x2000 /* ffs flag; indir buf is locked */
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#define IO_RANGELOCKED 0x4000 /* range locked */
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#define IO_DATASYNC 0x8000 /* do only data I/O synchronously */
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#define IO_SEQMAX 0x7F /* seq heuristic max value */
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#define IO_SEQSHIFT 16 /* seq heuristic in upper 16 bits */
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