On Mon, 2009-07-20 at 17:45 -0500, Eric Sandeen wrote: > Curt Wohlgemuth wrote: > > We've recently seen some interesting behavior with ftruncate() > > following a fallocate() call on ext4, and would like to know if this > > is intended or not. > > > > The sequence used from user space: > > > > fd = open() > > fallocate(fd, FALLOC_FL_KEEP_SIZE, 8MB) > > write(fd, buf, 64KB) > > ftruncate(fd, 64KB) > > close(fd) > > > > Since inode_setattr() only does something if the input size is not the > > same as inode->i_size, the ftruncate() call above does nothing; no > > blocks from the fallocate() are freed up. > > > > Yes, removing the KEEP_SIZE flag gets the behavior I'm expecting, but > > KEEP_SIZE is quite convenient in recovering from errors. > > > > I would have thought that ftruncate() would alter i_disksize even if > > this value is different from i_size. > > > > Any comments? I looked at other Linux file systems, and none that I > > saw that support fallocate() have this issue. > > > > Thanks, > > Curt > > Yep, I think you've found a bug, I will look into this soon unless > someone beats me to it :) I've spent a little while today digging into this. My guess (only a guess at this point until I have a chance to prove it) is that i_disksize should be updated by fallocate() even when KEEP_SIZE is specified. It's currently not updated in that case. It's my understanding that i_disksize should be the real allocation, right? While i_size is the size that has actually been used? If so, then setting i_disksize is probably what's missing. -- Frank Mayhar <fmayhar@xxxxxxxxxx> Google, Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
