On Thursday, November 02, 2017 10:38:49 AM Ngie Cooper wrote: > > > On Nov 2, 2017, at 06:49, Andriy Gapon <[email protected]> wrote: > > > > Author: avg > > Date: Thu Nov 2 13:49:08 2017 > > New Revision: 325320 > > URL: https://svnweb.freebsd.org/changeset/base/325320 > > > > Log: > > Disable posix_fallocate(2) for ZFS > > > > The generic (naive) implementation of posix_fallocate cannot provide the > > standard mandated guarantee that overwrites would never fail due to the > > lack > > of free space. The fundamental reason is the copy-on-write architecture > > of ZFS. Other features like compression and deduplication can also > > increase the size difference between the (pre-)allocated dummy content > > and the future content. > > > > So, until ZFS can properly implement the feature it's better to report > > that it is unsupported rather than providing an ersatz implementation. > > Please note that EINVAL is used to report that the underlying file system > > does not support the operation (POSIX.1-2008). > > > > illumos and ZoL seem to do the same. > > > > MFC after: 3 weeks > > Sponsored by: Panzura > > It’d be nice if it worked though and was reported via the file system. Posix > suggests it should be, as of 2013: http://austingroupbugs.net/view.php?id=687 > . > > Need to go poking around and see what’s in freebsd later on tonight. Bug > filed: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=223383 .
The austingroup link is just about adding a new pathconf() variable. posix_fallocate() would seem to be fundamentally incompatible with COW filesystems and can never work reliably for those. Even if you reserved N free blocks somehow until the first write, that doesn't allow multiple writes to the same file blocks while avoiding block allocation. fallocate only makes sense for overwriting filesystems like UFS. -- John Baldwin _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "[email protected]"
