On Wed, 23 Nov 2011 07:27:43 -0500 Theodore Tso <tytso@xxxxxxx> wrote: > >> > >> Maybe this is not that big problem as SIGKILL is considered be to > >> destructive already. > > > > Yeah, I have dim dark memories that there are subtle problems with > > interrupting write(). Linus might remember. (err, you're sending 600-column emails) > The big one is that you're lucky if application programmers check the > return values of write(2), and if they do, it's likely they will only > check for error returns and not necessarily for partial writes --- > since no other Unix-like or Linux-like system has ever returned partial > reads or writes for files except in error conditions. We've barely > gotten them trained to check for partial writes and reads with TCP > connections and character devices, but I wouldn't bet on application > programmers getting things right for files. > > Still, if it's ***only*** for SIGKILL, we'll probably be OK, since > for that one case there's no chance userspace can intercept the signal, > so it can't do any recovery anyway. (I could imagine some HPC program > doing a massive 2GB write, and some user of that program depending on > the fact that he can kill it at a predefined place by sending a SIGKILL > and knowing that the file would be written up to that 2GB chunk --- but > that's clearly an edge situation, as opposed to something that would > effect most GNOME and KDE apps.) We just need to make sure we never try > to do this for any other signal that could be caught, such as SIGINT or > SIGQUIT or (worse yet) SIGTSTP. That it is a fatal SIGKILL means that the *current* application doesn't care. But other processes will sometimes notice this change. Previously if an app did write(file, 128k) and was hit with SIGKILL, it would write either 0 bytes or 128k bytes. Now, it can write 36k bytes, yes? If the target file consisted of a stream of 128k records then the user will claim, with some justification, that Linux corrupted it. Dunno. People do lots of weird and flakey things. I have a suspicion that we'll be hearing back from them about this change. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
