Bug in Samba's implementation of FSCTL_QUERY_ALLOCATED_RANGES?

[David Howells]

ronnie sahlberg <ronniesahlberg at gmail.com> wrote:

> On Thu, 23 May 2024 at 14:54, David Disseldorp <ddiss at samba.org> wrote:
> It might be best to just ignore tests that fail in this area. And just
> accept that some things, at best, is a best-effort approximation.
> (as long as dataloss does not happen, of course. That is never acceptable)
> At the end of the day it is a lot of guesswork and trying to fit a
> square peg (unpredictable ntfs behavior) into a round hole (linux vfs
> api).

The problem is that it essentially renders SEEK_DATA/SEEK_HOLE unusable for
applications on cifs.  If there's more than one extent above the starting
position, they'll fail with EIO.  The only way to do it is to provide for a
sufficiently large buffer to accommodate however many extents that there are
(and there could be millions, in theory) in order to get just the first one.

David