fs/9p: remove writeback fid and fix per-file modes

This patch removes the creating of an additional writeback_fid
for opened files.  The patch addresses problems when files
were opened write-only or getattr on files with dirty caches.

This patch also incorporates information about cache behavior
in the fid for every file.  This allows us to reflect cache
behavior from mount flags, open mode, and information from
the server to inform readahead and writeback behavior.

This includes adding support for a 9p semantic that qid.version==0
is used to mark a file as non-cachable which is important for
synthetic files.  This may have a side-effect of not supporting
caching on certain legacy file servers that do not properly set
qid.version.  There is also now a mount flag which can disable
the qid.version behavior.

Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>

1 files changed, 12 insertions, 10 deletions

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index 6f46d7e4c750..211165430a8a 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -57,8 +57,6 @@ static void v9fs_issue_read(struct netfs_io_subrequest *subreq)
  */
 static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file)
 {
-	struct inode *inode = file_inode(file);
-	struct v9fs_inode *v9inode = V9FS_I(inode);
 	struct p9_fid *fid = file->private_data;
 
 	BUG_ON(!fid);
@@ -66,11 +64,8 @@ static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file)
 	/* we might need to read from a fid that was opened write-only
 	 * for read-modify-write of page cache, use the writeback fid
 	 * for that */
-	if (rreq->origin == NETFS_READ_FOR_WRITE &&
-			(fid->mode & O_ACCMODE) == O_WRONLY) {
-		fid = v9inode->writeback_fid;
-		BUG_ON(!fid);
-	}
+	WARN_ON(rreq->origin == NETFS_READ_FOR_WRITE &&
+			!(fid->mode & P9_ORDWR));
 
 	p9_fid_get(fid);
 	rreq->netfs_priv = fid;
@@ -164,6 +159,7 @@ static int v9fs_vfs_write_folio_locked(struct folio *folio)
 	loff_t i_size = i_size_read(inode);
 	struct iov_iter from;
 	size_t len = folio_size(folio);
+	struct p9_fid *writeback_fid;
 	int err;
 
 	if (start >= i_size)
@@ -173,13 +169,17 @@ static int v9fs_vfs_write_folio_locked(struct folio *folio)
 
 	iov_iter_xarray(&from, ITER_SOURCE, &folio_mapping(folio)->i_pages, start, len);
 
-	/* We should have writeback_fid always set */
-	BUG_ON(!v9inode->writeback_fid);
+	writeback_fid = v9fs_fid_find_inode(inode, true, INVALID_UID, true);
+	if (!writeback_fid) {
+		WARN_ONCE(1, "folio expected an open fid inode->i_private=%p\n",
+			inode->i_private);
+		return -EINVAL;
+	}
 
 	folio_wait_fscache(folio);
 	folio_start_writeback(folio);
 
-	p9_client_write(v9inode->writeback_fid, start, &from, &err);
+	p9_client_write(writeback_fid, start, &from, &err);
 
 	if (err == 0 &&
 	    fscache_cookie_enabled(cookie) &&
@@ -192,6 +192,8 @@ static int v9fs_vfs_write_folio_locked(struct folio *folio)
 	}
 
 	folio_end_writeback(folio);
+	p9_fid_put(writeback_fid);
+
 	return err;
 }