Re: [PATCH] Implement fallocate

[David Chinner <dgc@xxxxxxx>]

On Thu, Nov 01, 2007 at 12:15:45PM +1100, Lachlan McIlroy wrote:
> >+    xfs_ilock(XFS_I(inode), XFS_IOLOCK_EXCL);
> >+    error = xfs_change_file_space(XFS_I(inode), XFS_IOC_RESVSP, &bf,
> >+                                            0, NULL, ATTR_NOLOCK);
> >+    if (!error && !(mode & FALLOC_FL_KEEP_SIZE) &&
> >+        offset + len > i_size_read(inode))
> >+            new_size = offset + len;
> >+
> >+    /* Change file size if needed */
> >+    if (new_size) {
> >+            bhv_vattr_t     va;
> >+
> >+            va.va_mask = XFS_AT_SIZE;
> >+            va.va_size = new_size;
> >+            error = xfs_setattr(XFS_I(inode), &va, ATTR_NOLOCK, NULL);
> >+    }
> 
> Is it necessary to call xfs_setattr() here?  Could we just do an explicit
> call to xfs_zero_eof(), set the new size, set i_update_core/size and mark
> the inode dirty?  Hmmm, then again, that approach wouldn't be as clean as
> above.

And it also violates the atomicity that posix_fallocate is supposed
to provide. i.e. if it returns success, the change of file size must
be permanent. i.e. the change of size needs to be recorded in a
transaction. Hence we need to call xfs_setattr....

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group