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Subject[PATCH 4.17 041/220] fuse: atomic_o_trunc should truncate pagecache
Date
4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@redhat.com>

commit df0e91d488276086bc07da2e389986cae0048c37 upstream.

Fuse has an "atomic_o_trunc" mode, where userspace filesystem uses the
O_TRUNC flag in the OPEN request to truncate the file atomically with the
open.

In this mode there's no need to send a SETATTR request to userspace after
the open, so fuse_do_setattr() checks this mode and returns. But this
misses the important step of truncating the pagecache.

Add the missing parts of truncation to the ATTR_OPEN branch.

Reported-by: Chad Austin <chadaustin@fb.com>
Fixes: 6ff958edbf39 ("fuse: add atomic open+truncate support")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/fuse/dir.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1629,8 +1629,19 @@ int fuse_do_setattr(struct dentry *dentr
return err;

if (attr->ia_valid & ATTR_OPEN) {
- if (fc->atomic_o_trunc)
+ /* This is coming from open(..., ... | O_TRUNC); */
+ WARN_ON(!(attr->ia_valid & ATTR_SIZE));
+ WARN_ON(attr->ia_size != 0);
+ if (fc->atomic_o_trunc) {
+ /*
+ * No need to send request to userspace, since actual
+ * truncation has already been done by OPEN. But still
+ * need to truncate page cache.
+ */
+ i_size_write(inode, 0);
+ truncate_pagecache(inode, 0);
return 0;
+ }
file = NULL;
}


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