Add SEEK_DATA/SEEK_HOLE to lseek()/llseek()

The approach taken was the rework zfs_holey() as little as
possible and then just wrap the code as needed to ensure
correct locking and error handling.

Tested with xfstests 285 and 286.  All tests pass except for
7-9 of 285 which try to reserve blocks first via fallocate(2)
and fail because fallocate(2) is not yet supported.

Note that the filp->f_lock spinlock did not exist prior to
Linux 2.6.30, but we avoid the need for autotools check by
virtue of the fact that SEEK_DATA/SEEK_HOLE support was not
added until Linux 3.1.

An autoconf check was added for lseek_execute() which is
currently a private function but the expectation is that it
will be exported perhaps as early as Linux 3.11.

Reviewed-by: Richard Laager <[email protected]>
Signed-off-by: Richard Yao <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #1384

2 files changed, 50 insertions, 11 deletions

diff --git a/module/zfs/zfs_vnops.c b/module/zfs/zfs_vnops.c
index 5a9c96334..3c3e8db4b 100644
--- a/module/zfs/zfs_vnops.c
+++ b/module/zfs/zfs_vnops.c
@@ -240,15 +240,15 @@ zfs_close(struct inode *ip, int flag, cred_t *cr)
 }
 EXPORT_SYMBOL(zfs_close);
 
-#if 0
+#if defined(SEEK_HOLE) && defined(SEEK_DATA)
 /*
- * Lseek support for finding holes (cmd == _FIO_SEEK_HOLE) and
- * data (cmd == _FIO_SEEK_DATA). "off" is an in/out parameter.
+ * Lseek support for finding holes (cmd == SEEK_HOLE) and
+ * data (cmd == SEEK_DATA). "off" is an in/out parameter.
  */
 static int
-zfs_holey(vnode_t *vp, int cmd, offset_t *off)
+zfs_holey_common(struct inode *ip, int cmd, loff_t *off)
 {
-	znode_t	*zp = VTOZ(vp);
+	znode_t	*zp = ITOZ(ip);
 	uint64_t noff = (uint64_t)*off; /* new offset */
 	uint64_t file_sz;
 	int error;
@@ -256,15 +256,15 @@ zfs_holey(vnode_t *vp, int cmd, offset_t *off)
 
 	file_sz = zp->z_size;
 	if (noff >= file_sz)  {
-		return (SET_ERROR(ENXIO));
+		return (ENXIO);
 	}
 
-	if (cmd == _FIO_SEEK_HOLE)
+	if (cmd == SEEK_HOLE)
 		hole = B_TRUE;
 	else
 		hole = B_FALSE;
 
-	error = dmu_offset_next(zp->z_zfsvfs->z_os, zp->z_id, hole, &noff);
+	error = dmu_offset_next(ZTOZSB(zp)->z_os, zp->z_id, hole, &noff);
 
 	/* end of file? */
 	if ((error == ESRCH) || (noff > file_sz)) {
@@ -275,7 +275,7 @@ zfs_holey(vnode_t *vp, int cmd, offset_t *off)
 			*off = file_sz;
 			return (0);
 		}
-		return (SET_ERROR(ENXIO));
+		return (ENXIO);
 	}
 
 	if (noff < *off)
@@ -283,7 +283,24 @@ zfs_holey(vnode_t *vp, int cmd, offset_t *off)
 	*off = noff;
 	return (error);
 }
-#endif
+
+int
+zfs_holey(struct inode *ip, int cmd, loff_t *off)
+{
+	znode_t	*zp = ITOZ(ip);
+	zfs_sb_t *zsb = ITOZSB(ip);
+	int error;
+
+	ZFS_ENTER(zsb);
+	ZFS_VERIFY_ZP(zp);
+
+	error = zfs_holey_common(ip, cmd, off);
+
+	ZFS_EXIT(zsb);
+	return (error);
+}
+EXPORT_SYMBOL(zfs_holey);
+#endif /* SEEK_HOLE && SEEK_DATA */
 
 #if defined(_KERNEL)
 /*
diff --git a/module/zfs/zpl_file.c b/module/zfs/zpl_file.c
index c6d97db50..ebae6bfe2 100644
--- a/module/zfs/zpl_file.c
+++ b/module/zfs/zpl_file.c
@@ -235,6 +235,28 @@ zpl_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos)
 	return (wrote);
 }
 
+static loff_t
+zpl_llseek(struct file *filp, loff_t offset, int whence)
+{
+#if defined(SEEK_HOLE) && defined(SEEK_DATA)
+	if (whence == SEEK_DATA || whence == SEEK_HOLE) {
+		struct inode *ip = filp->f_mapping->host;
+		loff_t maxbytes = ip->i_sb->s_maxbytes;
+		loff_t error;
+
+		spl_inode_lock(ip);
+		error = -zfs_holey(ip, whence, &offset);
+		if (error == 0)
+			error = lseek_execute(filp, ip, offset, maxbytes);
+		spl_inode_unlock(ip);
+
+		return (error);
+	}
+#endif /* SEEK_HOLE && SEEK_DATA */
+
+	return generic_file_llseek(filp, offset, whence);
+}
+
 /*
  * It's worth taking a moment to describe how mmap is implemented
  * for zfs because it differs considerably from other Linux filesystems.
@@ -464,7 +486,7 @@ const struct address_space_operations zpl_address_space_operations = {
 const struct file_operations zpl_file_operations = {
 	.open		= zpl_open,
 	.release	= zpl_release,
-	.llseek		= generic_file_llseek,
+	.llseek		= zpl_llseek,
 	.read		= zpl_read,
 	.write		= zpl_write,
 	.mmap		= zpl_mmap,