[v3] fscache, cachefiles: Fix resize handling

[Alex Markuze]

Hi David,

Reviewed this on your netfs-next-5 tree. The resize helper it changes is not in our testing branch.

For Ceph this is the right split. ceph_fill_file_size() stores the new i_size before __ceph_do_pending_vmtruncate() trims the page cache and the cookie, so the worker can no longer see that the file shrank. i_truncate_shrank records size < isize at the truncate_seq bump. Without that, a truncate that is still above the stale cache size takes the grow path and leaves the backing tail in place.

IMHO the same flag is right for the other filesystems. AFS, 9p, and cifs_resize_file_locked() still have the old size at the call, so shrank is a direct comparison. The grow paths pass false, collapse passes true, and cachefiles shortens only when the caller says the file shrank and the backing file is actually larger.

Reviewed-by: Alex Markuze <amarkuze at redhat.com>

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Alex Markuze