ceph: set i_head_snapc when getting CEPH_CAP_FILE_WR reference

In most cases that snap context is needed, we are holding
reference of CEPH_CAP_FILE_WR. So we can set ceph inode's
i_head_snapc when getting the CEPH_CAP_FILE_WR reference,
and make codes get snap context from i_head_snapc. This makes
the code simpler.

Another benefit of this change is that we can handle snap
notification more elegantly. Especially when snap context
is updated while someone else is doing write. The old queue
cap_snap code may set cap_snap's context to ether the old
context or the new snap context, depending on if i_head_snapc
is set. The new queue capp_snap code always set cap_snap's
context to the old snap context.

Signed-off-by: Yan, Zheng <zyan@redhat.com>

1 files changed, 23 insertions, 8 deletions

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 777eb21d556f..0a76a370d798 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -557,13 +557,13 @@ static void ceph_sync_write_unsafe(struct ceph_osd_request *req, bool unsafe)
  * objects, rollback on failure, etc.)
  */
 static ssize_t
-ceph_sync_direct_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos)
+ceph_sync_direct_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
+		       struct ceph_snap_context *snapc)
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(file);
 	struct ceph_inode_info *ci = ceph_inode(inode);
 	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
-	struct ceph_snap_context *snapc;
 	struct ceph_vino vino;
 	struct ceph_osd_request *req;
 	struct page **pages;
@@ -600,7 +600,6 @@ ceph_sync_direct_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos)
 		size_t start;
 		ssize_t n;
 
-		snapc = ci->i_snap_realm->cached_context;
 		vino = ceph_vino(inode);
 		req = ceph_osdc_new_request(&fsc->client->osdc, &ci->i_layout,
 					    vino, pos, &len, 0,
@@ -674,13 +673,13 @@ ceph_sync_direct_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos)
  * objects, rollback on failure, etc.)
  */
 static ssize_t
-ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos)
+ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
+		struct ceph_snap_context *snapc)
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(file);
 	struct ceph_inode_info *ci = ceph_inode(inode);
 	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
-	struct ceph_snap_context *snapc;
 	struct ceph_vino vino;
 	struct ceph_osd_request *req;
 	struct page **pages;
@@ -717,7 +716,6 @@ ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos)
 		size_t left;
 		int n;
 
-		snapc = ci->i_snap_realm->cached_context;
 		vino = ceph_vino(inode);
 		req = ceph_osdc_new_request(&fsc->client->osdc, &ci->i_layout,
 					    vino, pos, &len, 0, 1,
@@ -996,14 +994,30 @@ retry_snap:
 
 	if ((got & (CEPH_CAP_FILE_BUFFER|CEPH_CAP_FILE_LAZYIO)) == 0 ||
 	    (iocb->ki_flags & IOCB_DIRECT) || (fi->flags & CEPH_F_SYNC)) {
+		struct ceph_snap_context *snapc;
 		struct iov_iter data;
 		mutex_unlock(&inode->i_mutex);
+
+		spin_lock(&ci->i_ceph_lock);
+		if (__ceph_have_pending_cap_snap(ci)) {
+			struct ceph_cap_snap *capsnap =
+					list_last_entry(&ci->i_cap_snaps,
+							struct ceph_cap_snap,
+							ci_item);
+			snapc = ceph_get_snap_context(capsnap->context);
+		} else {
+			BUG_ON(!ci->i_head_snapc);
+			snapc = ceph_get_snap_context(ci->i_head_snapc);
+		}
+		spin_unlock(&ci->i_ceph_lock);
+
 		/* we might need to revert back to that point */
 		data = *from;
 		if (iocb->ki_flags & IOCB_DIRECT)
-			written = ceph_sync_direct_write(iocb, &data, pos);
+			written = ceph_sync_direct_write(iocb, &data, pos,
+							 snapc);
 		else
-			written = ceph_sync_write(iocb, &data, pos);
+			written = ceph_sync_write(iocb, &data, pos, snapc);
 		if (written == -EOLDSNAPC) {
 			dout("aio_write %p %llx.%llx %llu~%u"
 				"got EOLDSNAPC, retrying\n",
@@ -1014,6 +1028,7 @@ retry_snap:
 		}
 		if (written > 0)
 			iov_iter_advance(from, written);
+		ceph_put_snap_context(snapc);
 	} else {
 		loff_t old_size = inode->i_size;
 		/*