Date: Wed, 18 May 2016 00:22:27 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Bruce Evans <brde@optusnet.com.au> Cc: fs@freebsd.org Subject: Re: quick fix for slow directory shrinking in ffs Message-ID: <20160517212227.GE89104@kib.kiev.ua> In-Reply-To: <20160518052656.R5764@besplex.bde.org> References: <20160517072705.F2157@besplex.bde.org> <20160517082050.GX89104@kib.kiev.ua> <20160517192933.U4573@besplex.bde.org> <20160517111715.GC89104@kib.kiev.ua> <20160518035413.L4357@besplex.bde.org> <20160518052656.R5764@besplex.bde.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, May 18, 2016 at 05:40:07AM +1000, Bruce Evans wrote:
> Also, ftruncate() seems to be broken. POSIX doesn't seem to require it
> to honor O_SYNC, but POLA requires this. But there is no VOP_TRUNCATE();
> truncation is done using VOP_SETATTR() and there is no way to pass down
> the O_SYNC flag to it; in practice, ffs just does UFS_TRUNCATE() without
> IO_SYNC.
>
> This makes a difference mainly for async mounts with my fixes to honor
> IO_SYNC in ffs_update(). With async mounts, consistency of the file
> system is not guaranteed but O_SYNC for a file should at least cause
> all of the file data and most of its metdata to be written. Not syncing
> for ftruncate() unnecessarily loses metadata writes. With !async mounts,
> consistency of the file system is partly guaranteed and lost metadata
> writes for ftruncate() shouldn't affect this -- they should just lose
> the ftruncate() atomically.
>
> vfs could do an fsync() after VOP_SETATTR() for the O_SYNC case. This
> reduces the race window.
vattr already has the va_vaflags field. It is trivial to add flag there
requesting O_SYNC behaviour. Of course, other updates could also
honour VA_SYNC, but this is for later. Like this:
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index 0a3a88a..1e42a3d 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -1314,6 +1314,8 @@ vn_truncate(struct file *fp, off_t length, struct ucred *active_cred,
if (error == 0) {
VATTR_NULL(&vattr);
vattr.va_size = length;
+ if ((fp->f_flag & O_FSYNC) != 0)
+ vattr.va_vaflags |= VA_SYNC;
error = VOP_SETATTR(vp, &vattr, fp->f_cred);
}
out:
diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h
index e82f6ee..41ec7f7 100644
--- a/sys/sys/vnode.h
+++ b/sys/sys/vnode.h
@@ -286,6 +286,7 @@ struct vattr {
*/
#define VA_UTIMES_NULL 0x01 /* utimes argument was NULL */
#define VA_EXCLUSIVE 0x02 /* exclusive create request */
+#define VA_SYNC 0x04 /* O_SYNC truncation */
/*
* Flags for ioflag. (high 16 bits used to ask for read-ahead and
diff --git a/sys/ufs/ufs/ufs_vnops.c b/sys/ufs/ufs/ufs_vnops.c
index c0729f8..83df347 100644
--- a/sys/ufs/ufs/ufs_vnops.c
+++ b/sys/ufs/ufs/ufs_vnops.c
@@ -625,7 +625,8 @@ ufs_setattr(ap)
*/
return (0);
}
- if ((error = UFS_TRUNCATE(vp, vap->va_size, IO_NORMAL,
+ if ((error = UFS_TRUNCATE(vp, vap->va_size, IO_NORMAL |
+ ((vap->va_vaflags & VA_SYNC) != 0 ? IO_SYNC : 0),
cred)) != 0)
return (error);
}
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20160517212227.GE89104>