Discussion:
[PATCH] Btrfs: ensure send always works on roots without orphans
(too old to reply)
Filipe Manana
2014-10-21 10:11:41 UTC
Permalink
Move the logic from the snapshot creation ioctl into send. This avoids
doing the transaction commit if send isn't used, and ensures that if
a crash/reboot happens after the transaction commit that created the
snapshot and before the transaction commit that switched the commit
root, send will not get a commit root that differs from the main root
(that has orphan items).

Signed-off-by: Filipe Manana <***@suse.com>
---
fs/btrfs/ioctl.c | 29 -----------------------------
fs/btrfs/send.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 49 insertions(+), 29 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 33c80f5..994c573 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -717,35 +717,6 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
if (ret)
goto fail;

- /*
- * If orphan cleanup did remove any orphans, it means the tree was
- * modified and therefore the commit root is not the same as the
- * current root anymore. This is a problem, because send uses the
- * commit root and therefore can see inode items that don't exist
- * in the current root anymore, and for example make calls to
- * btrfs_iget, which will do tree lookups based on the current root
- * and not on the commit root. Those lookups will fail, returning a
- * -ESTALE error, and making send fail with that error. So make sure
- * a send does not see any orphans we have just removed, and that it
- * will see the same inodes regardless of whether a transaction
- * commit happened before it started (meaning that the commit root
- * will be the same as the current root) or not.
- */
- if (readonly && pending_snapshot->snap->node !=
- pending_snapshot->snap->commit_root) {
- trans = btrfs_join_transaction(pending_snapshot->snap);
- if (IS_ERR(trans) && PTR_ERR(trans) != -ENOENT) {
- ret = PTR_ERR(trans);
- goto fail;
- }
- if (!IS_ERR(trans)) {
- ret = btrfs_commit_transaction(trans,
- pending_snapshot->snap);
- if (ret)
- goto fail;
- }
- }
-
inode = btrfs_lookup_dentry(dentry->d_parent->d_inode, dentry);
if (IS_ERR(inode)) {
ret = PTR_ERR(inode);
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 874828d..804432d 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -5507,6 +5507,51 @@ out:
return ret;
}

+/*
+ * If orphan cleanup did remove any orphans from a root, it means the tree
+ * was modified and therefore the commit root is not the same as the current
+ * root anymore. This is a problem, because send uses the commit root and
+ * therefore can see inode items that don't exist in the current root anymore,
+ * and for example make calls to btrfs_iget, which will do tree lookups based
+ * on the current root and not on the commit root. Those lookups will fail,
+ * returning a -ESTALE error, and making send fail with that error. So make
+ * sure a send does not see any orphans we have just removed, and that it will
+ * see the same inodes regardless of whether a transaction commit happened
+ * before it started (meaning that the commit root will be the same as the
+ * current root) or not.
+ */
+static int ensure_commit_roots_uptodate(struct send_ctx *sctx)
+{
+ int i;
+ struct btrfs_trans_handle *trans = NULL;
+
+again:
+ if (sctx->parent_root &&
+ sctx->parent_root->node != sctx->parent_root->commit_root)
+ goto commit_trans;
+
+ for (i = 0; i < sctx->clone_roots_cnt; i++)
+ if (sctx->clone_roots[i].root->node !=
+ sctx->clone_roots[i].root->commit_root)
+ goto commit_trans;
+
+ if (trans)
+ return btrfs_end_transaction(trans, sctx->send_root);
+
+ return 0;
+
+commit_trans:
+ /* Use any root, all fs roots will get their commit roots updated. */
+ if (!trans) {
+ trans = btrfs_join_transaction(sctx->send_root);
+ if (IS_ERR(trans))
+ return PTR_ERR(trans);
+ goto again;
+ }
+
+ return btrfs_commit_transaction(trans, sctx->send_root);
+}
+
static void btrfs_root_dec_send_in_progress(struct btrfs_root* root)
{
spin_lock(&root->root_item_lock);
@@ -5728,6 +5773,10 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
NULL);
sort_clone_roots = 1;

+ ret = ensure_commit_roots_uptodate(sctx);
+ if (ret)
+ goto out;
+
current->journal_info = BTRFS_SEND_TRANS_STUB;
ret = send_subvol(sctx);
current->journal_info = NULL;
--
1.9.1

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