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Subject[PATCH v2 5/5] btrfs: enable swap file support
Date
Implement the swap file a_ops on btrfs. Activation simply checks for a usable
swap file: it must be fully allocated (no holes), support direct I/O (so no
compressed or inline extents) and should be nocow (I'm not sure about that last
one).

Signed-off-by: Omar Sandoval <osandov@osandov.com>
---
fs/btrfs/inode.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 71 insertions(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index d23362f..b8fd36b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9442,6 +9442,75 @@ out_inode:

}

+static int btrfs_swap_activate(struct swap_info_struct *sis, struct file *file,
+ sector_t *span)
+{
+ struct inode *inode = file_inode(file);
+ struct btrfs_inode *ip = BTRFS_I(inode);
+ int ret = 0;
+ u64 isize = inode->i_size;
+ struct extent_state *cached_state = NULL;
+ struct extent_map *em;
+ u64 start, len;
+
+ if (ip->flags & BTRFS_INODE_COMPRESS) {
+ /* Can't do direct I/O on a compressed file. */
+ pr_err("BTRFS: swapfile is compressed");
+ return -EINVAL;
+ }
+ if (!(ip->flags & BTRFS_INODE_NODATACOW)) {
+ /* The swap file can't be copy-on-write. */
+ pr_err("BTRFS: swapfile is copy-on-write");
+ return -EINVAL;
+ }
+
+ lock_extent_bits(&ip->io_tree, 0, isize - 1, 0, &cached_state);
+
+ /*
+ * All of the extents must be allocated and support direct I/O. Inline
+ * extents and compressed extents fall back to buffered I/O, so those
+ * are no good.
+ */
+ start = 0;
+ while (start < isize) {
+ len = isize - start;
+ em = btrfs_get_extent(inode, NULL, 0, start, len, 0);
+ if (IS_ERR(em)) {
+ ret = PTR_ERR(em);
+ goto out;
+ }
+
+ if (test_bit(EXTENT_FLAG_VACANCY, &em->flags) ||
+ em->block_start == EXTENT_MAP_HOLE) {
+ pr_err("BTRFS: swapfile has holes");
+ ret = -EINVAL;
+ goto out;
+ }
+ if (em->block_start == EXTENT_MAP_INLINE) {
+ pr_err("BTRFS: swapfile is inline");
+ ret = -EINVAL;
+ goto out;
+ }
+ if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags)) {
+ pr_err("BTRFS: swapfile is compresed");
+ ret = -EINVAL;
+ goto out;
+ }
+
+ start = extent_map_end(em);
+ free_extent_map(em);
+ }
+
+out:
+ unlock_extent_cached(&ip->io_tree, 0, isize - 1, &cached_state,
+ GFP_NOFS);
+ return ret;
+}
+
+static void btrfs_swap_deactivate(struct file *file)
+{
+}
+
static const struct inode_operations btrfs_dir_inode_operations = {
.getattr = btrfs_getattr,
.lookup = btrfs_lookup,
@@ -9519,6 +9588,8 @@ static const struct address_space_operations btrfs_aops = {
.releasepage = btrfs_releasepage,
.set_page_dirty = btrfs_set_page_dirty,
.error_remove_page = generic_error_remove_page,
+ .swap_activate = btrfs_swap_activate,
+ .swap_deactivate = btrfs_swap_deactivate,
};

static const struct address_space_operations btrfs_symlink_aops = {
--
2.1.3


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