Extend the KPI to lock and unlock f_offset member of struct file. It

now fully encapsulates all accesses to f_offset, and extends f_offset
locking to other consumers that need it, in particular, to lseek() and
variants of getdirentries().

Ensure that on 32bit architectures f_offset, which is 64bit quantity,
always read and written under the mtxpool protection. This fixes
apparently easy to trigger race when parallel lseek()s or lseek() and
read/write could destroy file offset.

The already broken ABI emulations, including iBCS and SysV, are not
converted (yet).

Tested by:	pho
No objections from:	jhb
MFC after:    3 weeks

1 files changed, 2 insertions, 5 deletions

diff --git a/sys/ufs/ffs/ffs_alloc.c b/sys/ufs/ffs/ffs_alloc.c
index 68ea172..2b3740d 100644
--- a/sys/ufs/ffs/ffs_alloc.c
+++ b/sys/ufs/ffs/ffs_alloc.c
@@ -2865,10 +2865,9 @@ buffered_write(fp, uio, active_cred, flags, td)
 	if (ip->i_devvp != devvp)
 		return (EINVAL);
 	fs = ip->i_fs;
+	foffset_lock_uio(fp, uio, flags);
 	vfslocked = VFS_LOCK_GIANT(ip->i_vnode->v_mount);
 	vn_lock(devvp, LK_EXCLUSIVE | LK_RETRY);
-	if ((flags & FOF_OFFSET) == 0)
-		uio->uio_offset = fp->f_offset;
 #ifdef DEBUG
 	if (fsckcmds) {
 		printf("%s: buffered write for block %jd\n",
@@ -2893,11 +2892,9 @@ buffered_write(fp, uio, active_cred, flags, td)
 		goto out;
 	}
 	error = bwrite(bp);
-	if ((flags & FOF_OFFSET) == 0)
-		fp->f_offset = uio->uio_offset;
-	fp->f_nextoff = uio->uio_offset;
 out:
 	VOP_UNLOCK(devvp, 0);
 	VFS_UNLOCK_GIANT(vfslocked);
+	foffset_unlock_uio(fp, uio, flags | FOF_NEXTOFF);
 	return (error);
 }