On Wed, Jun 29, 2011 at 04:53:07PM +1000, Dave Chinner wrote:On Tue, Jun 28, 2011 at 11:33:19AM -0400, Josef Bacik wrote:The discussion leading up to the resurrection of SEEK_HOLE/SEEK_DATAThis is a test to make sure seek_data/seek_hole is acting like it does onSo I just looked at this with an eye to validating an XFS
Solaris. It will check to see if the fs supports finding a hole or not and will
adjust as necessary.
implementation, and I came up with this list of stuff that the test
does not cover that I'd need to test in some way:
- files with clean unwritten extents. Are they a hole or
data? What's SEEK_DATA supposed to return on layout like
hole-unwritten-data? i.e. needs to add fallocate to the
picture...
- files with dirty unwritten extents (i.e. dirty in memory,
not on disk). They are most definitely data, and most
filesystems will need a separate lookup path to detect
dirty unwritten ranges because the state is kept
separately (page cache vs extent cache). Plenty of scope
for filesystem specific bugs here so needs a roubust test.
was pretty much about that point. The conclusion based on the Sun
documentation and common sense was that SEEK_DATA may only consider
unwritten extents as hole if the filesystem has a way to distinguish
plain unwritten extents and those that have been dirtied. Else it
should be considered data.
Testing for making sure dirty preallocated areas aren't wrongly
reported sounds relatively easy, the rest falls into implementation
details, which imho is fine. Not reporting preallocated extents
as holes just is a quality of implementation issue and not a bug.