xfs: unshare a range of blocks via fallocate

Unshare all shared extents if the user calls fallocate with the new
unshare mode flag set, so that we can guarantee that a subsequent
write will not ENOSPC.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
[hch: pass inode instead of file to xfs_reflink_dirty_range,
      use iomap infrastructure for copy up]
Signed-off-by: Christoph Hellwig <hch@lst.de>

3 files changed, 267 insertions, 2 deletions

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 39fde9f51303..07f951dd2685 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -848,7 +848,7 @@ buffered:
 #define XFS_FALLOC_FL_SUPPORTED                                         \
                 (FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |           \
                  FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |      \
-                 FALLOC_FL_INSERT_RANGE)
+                 FALLOC_FL_INSERT_RANGE | FALLOC_FL_UNSHARE_RANGE)
 
 STATIC long
 xfs_file_fallocate(
@@ -938,9 +938,15 @@ xfs_file_fallocate(
 
                 if (mode & FALLOC_FL_ZERO_RANGE)
                         error = xfs_zero_file_space(ip, offset, len);
-                else
+                else {
+                        if (mode & FALLOC_FL_UNSHARE_RANGE) {
+                                error = xfs_reflink_unshare(ip, offset, len);
+                                if (error)
+                                        goto out_unlock;
+                        }
                         error = xfs_alloc_file_space(ip, offset, len,
                                                      XFS_BMAPI_PREALLOC);
+                }
                 if (error)
                         goto out_unlock;
         }
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 6b22669421b2..d4707e627a74 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1345,3 +1345,258 @@ out_error:
                 trace_xfs_reflink_remap_range_error(dest, error, _RET_IP_);
         return error;
 }
+
+/*
+ * The user wants to preemptively CoW all shared blocks in this file,
+ * which enables us to turn off the reflink flag.  Iterate all
+ * extents which are not prealloc/delalloc to see which ranges are
+ * mentioned in the refcount tree, then read those blocks into the
+ * pagecache, dirty them, fsync them back out, and then we can update
+ * the inode flag.  What happens if we run out of memory? :)
+ */
+STATIC int
+xfs_reflink_dirty_extents(
+        struct xfs_inode        *ip,
+        xfs_fileoff_t           fbno,
+        xfs_filblks_t           end,
+        xfs_off_t               isize)
+{
+        struct xfs_mount        *mp = ip->i_mount;
+        xfs_agnumber_t          agno;
+        xfs_agblock_t           agbno;
+        xfs_extlen_t            aglen;
+        xfs_agblock_t           rbno;
+        xfs_extlen_t            rlen;
+        xfs_off_t               fpos;
+        xfs_off_t               flen;
+        struct xfs_bmbt_irec    map[2];
+        int                     nmaps;
+        int                     error;
+
+        while (end - fbno > 0) {
+                nmaps = 1;
+                /*
+                 * Look for extents in the file.  Skip holes, delalloc, or
+                 * unwritten extents; they can't be reflinked.
+                 */
+                error = xfs_bmapi_read(ip, fbno, end - fbno, map, &nmaps, 0);
+                if (error)
+                        goto out;
+                if (nmaps == 0)
+                        break;
+                if (map[0].br_startblock == HOLESTARTBLOCK ||
+                    map[0].br_startblock == DELAYSTARTBLOCK ||
+                    ISUNWRITTEN(&map[0]))
+                        goto next;
+
+                map[1] = map[0];
+                while (map[1].br_blockcount) {
+                        agno = XFS_FSB_TO_AGNO(mp, map[1].br_startblock);
+                        agbno = XFS_FSB_TO_AGBNO(mp, map[1].br_startblock);
+                        aglen = map[1].br_blockcount;
+
+                        error = xfs_reflink_find_shared(mp, agno, agbno, aglen,
+                                        &rbno, &rlen, true);
+                        if (error)
+                                goto out;
+                        if (rbno == NULLAGBLOCK)
+                                break;
+
+                        /* Dirty the pages */
+                        xfs_iunlock(ip, XFS_ILOCK_EXCL);
+                        fpos = XFS_FSB_TO_B(mp, map[1].br_startoff +
+                                        (rbno - agbno));
+                        flen = XFS_FSB_TO_B(mp, rlen);
+                        if (fpos + flen > isize)
+                                flen = isize - fpos;
+                        error = iomap_file_dirty(VFS_I(ip), fpos, flen,
+                                        &xfs_iomap_ops);
+                        xfs_ilock(ip, XFS_ILOCK_EXCL);
+                        if (error)
+                                goto out;
+
+                        map[1].br_blockcount -= (rbno - agbno + rlen);
+                        map[1].br_startoff += (rbno - agbno + rlen);
+                        map[1].br_startblock += (rbno - agbno + rlen);
+                }
+
+next:
+                fbno = map[0].br_startoff + map[0].br_blockcount;
+        }
+out:
+        return error;
+}
+
+/* Clear the inode reflink flag if there are no shared extents. */
+int
+xfs_reflink_clear_inode_flag(
+        struct xfs_inode        *ip,
+        struct xfs_trans        **tpp)
+{
+        struct xfs_mount        *mp = ip->i_mount;
+        xfs_fileoff_t           fbno;
+        xfs_filblks_t           end;
+        xfs_agnumber_t          agno;
+        xfs_agblock_t           agbno;
+        xfs_extlen_t            aglen;
+        xfs_agblock_t           rbno;
+        xfs_extlen_t            rlen;
+        struct xfs_bmbt_irec    map[2];
+        int                     nmaps;
+        int                     error = 0;
+
+        if (!(ip->i_d.di_flags2 & XFS_DIFLAG2_REFLINK))
+                return 0;
+
+        fbno = 0;
+        end = XFS_B_TO_FSB(mp, i_size_read(VFS_I(ip)));
+        while (end - fbno > 0) {
+                nmaps = 1;
+                /*
+                 * Look for extents in the file.  Skip holes, delalloc, or
+                 * unwritten extents; they can't be reflinked.
+                 */
+                error = xfs_bmapi_read(ip, fbno, end - fbno, map, &nmaps, 0);
+                if (error)
+                        return error;
+                if (nmaps == 0)
+                        break;
+                if (map[0].br_startblock == HOLESTARTBLOCK ||
+                    map[0].br_startblock == DELAYSTARTBLOCK ||
+                    ISUNWRITTEN(&map[0]))
+                        goto next;
+
+                map[1] = map[0];
+                while (map[1].br_blockcount) {
+                        agno = XFS_FSB_TO_AGNO(mp, map[1].br_startblock);
+                        agbno = XFS_FSB_TO_AGBNO(mp, map[1].br_startblock);
+                        aglen = map[1].br_blockcount;
+
+                        error = xfs_reflink_find_shared(mp, agno, agbno, aglen,
+                                        &rbno, &rlen, false);
+                        if (error)
+                                return error;
+                        /* Is there still a shared block here? */
+                        if (rbno != NULLAGBLOCK)
+                                return 0;
+
+                        map[1].br_blockcount -= aglen;
+                        map[1].br_startoff += aglen;
+                        map[1].br_startblock += aglen;
+                }
+
+next:
+                fbno = map[0].br_startoff + map[0].br_blockcount;
+        }
+
+        /*
+         * We didn't find any shared blocks so turn off the reflink flag.
+         * First, get rid of any leftover CoW mappings.
+         */
+        error = xfs_reflink_cancel_cow_blocks(ip, tpp, 0, NULLFILEOFF);
+        if (error)
+                return error;
+
+        /* Clear the inode flag. */
+        trace_xfs_reflink_unset_inode_flag(ip);
+        ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
+        xfs_trans_ijoin(*tpp, ip, 0);
+        xfs_trans_log_inode(*tpp, ip, XFS_ILOG_CORE);
+
+        return error;
+}
+
+/*
+ * Clear the inode reflink flag if there are no shared extents and the size
+ * hasn't changed.
+ */
+STATIC int
+xfs_reflink_try_clear_inode_flag(
+        struct xfs_inode        *ip,
+        xfs_off_t               old_isize)
+{
+        struct xfs_mount        *mp = ip->i_mount;
+        struct xfs_trans        *tp;
+        int                     error = 0;
+
+        /* Start a rolling transaction to remove the mappings */
+        error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0, 0, &tp);
+        if (error)
+                return error;
+
+        xfs_ilock(ip, XFS_ILOCK_EXCL);
+        xfs_trans_ijoin(tp, ip, 0);
+
+        if (old_isize != i_size_read(VFS_I(ip)))
+                goto cancel;
+
+        error = xfs_reflink_clear_inode_flag(ip, &tp);
+        if (error)
+                goto cancel;
+
+        error = xfs_trans_commit(tp);
+        if (error)
+                goto out;
+
+        xfs_iunlock(ip, XFS_ILOCK_EXCL);
+        return 0;
+cancel:
+        xfs_trans_cancel(tp);
+out:
+        xfs_iunlock(ip, XFS_ILOCK_EXCL);
+        return error;
+}
+
+/*
+ * Pre-COW all shared blocks within a given byte range of a file and turn off
+ * the reflink flag if we unshare all of the file's blocks.
+ */
+int
+xfs_reflink_unshare(
+        struct xfs_inode        *ip,
+        xfs_off_t               offset,
+        xfs_off_t               len)
+{
+        struct xfs_mount        *mp = ip->i_mount;
+        xfs_fileoff_t           fbno;
+        xfs_filblks_t           end;
+        xfs_off_t               isize;
+        int                     error;
+
+        if (!xfs_is_reflink_inode(ip))
+                return 0;
+
+        trace_xfs_reflink_unshare(ip, offset, len);
+
+        inode_dio_wait(VFS_I(ip));
+
+        /* Try to CoW the selected ranges */
+        xfs_ilock(ip, XFS_ILOCK_EXCL);
+        fbno = XFS_B_TO_FSB(mp, offset);
+        isize = i_size_read(VFS_I(ip));
+        end = XFS_B_TO_FSB(mp, offset + len);
+        error = xfs_reflink_dirty_extents(ip, fbno, end, isize);
+        if (error)
+                goto out_unlock;
+        xfs_iunlock(ip, XFS_ILOCK_EXCL);
+
+        /* Wait for the IO to finish */
+        error = filemap_write_and_wait(VFS_I(ip)->i_mapping);
+        if (error)
+                goto out;
+
+        /* Turn off the reflink flag if we unshared the whole file */
+        if (offset == 0 && len == isize) {
+                error = xfs_reflink_try_clear_inode_flag(ip, isize);
+                if (error)
+                        goto out;
+        }
+
+        return 0;
+
+out_unlock:
+        xfs_iunlock(ip, XFS_ILOCK_EXCL);
+out:
+        trace_xfs_reflink_unshare_error(ip, error, _RET_IP_);
+        return error;
+}
diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
index df82b2049187..bade5a61f3b0 100644
--- a/fs/xfs/xfs_reflink.h
+++ b/fs/xfs/xfs_reflink.h
@@ -48,5 +48,9 @@ extern int xfs_reflink_recover_cow(struct xfs_mount *mp);
 extern int xfs_reflink_remap_range(struct xfs_inode *src, xfs_off_t srcoff,
                 struct xfs_inode *dest, xfs_off_t destoff, xfs_off_t len,
                 unsigned int flags);
+extern int xfs_reflink_clear_inode_flag(struct xfs_inode *ip,
+                struct xfs_trans **tpp);
+extern int xfs_reflink_unshare(struct xfs_inode *ip, xfs_off_t offset,
+                xfs_off_t len);
 
 #endif /* __XFS_REFLINK_H */