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authorChristoph Hellwig <hch@lst.de>2017-06-03 15:18:31 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-06-07 12:07:52 +0200
commite40c145c023db15a0504e95ac442f0e47c0a816d (patch)
tree0bec11fba02c7f976c55f05d0b9752d465bb39dd
parent0e542792a046c788f39ab13fcd68c7ba65930407 (diff)
downloadlinux-aarch64-e40c145c023db15a0504e95ac442f0e47c0a816d.tar.gz
xfs: xfs_trans_alloc_empty
This is a partial cherry-pick of commit e89c041338 ("xfs: implement the GETFSMAP ioctl"), which also adds this helper, and a great example of why feature patches should be properly split into their parts. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> [hch: split from the larger patch for -stable] Signed-off-by: Christoph Hellwig <hch@lst.de>
-rw-r--r--fs/xfs/xfs_trans.c22
-rw-r--r--fs/xfs/xfs_trans.h2
2 files changed, 24 insertions, 0 deletions
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 70f42ea86dfb..a280e126491f 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -263,6 +263,28 @@ xfs_trans_alloc(
}
/*
+ * Create an empty transaction with no reservation. This is a defensive
+ * mechanism for routines that query metadata without actually modifying
+ * them -- if the metadata being queried is somehow cross-linked (think a
+ * btree block pointer that points higher in the tree), we risk deadlock.
+ * However, blocks grabbed as part of a transaction can be re-grabbed.
+ * The verifiers will notice the corrupt block and the operation will fail
+ * back to userspace without deadlocking.
+ *
+ * Note the zero-length reservation; this transaction MUST be cancelled
+ * without any dirty data.
+ */
+int
+xfs_trans_alloc_empty(
+ struct xfs_mount *mp,
+ struct xfs_trans **tpp)
+{
+ struct xfs_trans_res resv = {0};
+
+ return xfs_trans_alloc(mp, &resv, 0, 0, XFS_TRANS_NO_WRITECOUNT, tpp);
+}
+
+/*
* Record the indicated change to the given field for application
* to the file system's superblock when the transaction commits.
* For now, just store the change in the transaction structure.
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index 61b7fbdd3ebd..98024cb933ef 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -159,6 +159,8 @@ typedef struct xfs_trans {
int xfs_trans_alloc(struct xfs_mount *mp, struct xfs_trans_res *resp,
uint blocks, uint rtextents, uint flags,
struct xfs_trans **tpp);
+int xfs_trans_alloc_empty(struct xfs_mount *mp,
+ struct xfs_trans **tpp);
void xfs_trans_mod_sb(xfs_trans_t *, uint, int64_t);
struct xfs_buf *xfs_trans_get_buf_map(struct xfs_trans *tp,