On Mon, Apr 27, 2015 at 9:22 AM, Rich Felker <[email protected]> wrote: > On Mon, Apr 27, 2015 at 09:17:31AM -0700, enh wrote: >> On Mon, Apr 27, 2015 at 9:11 AM, Rich Felker <[email protected]> wrote: >> > On Mon, Apr 27, 2015 at 08:36:53AM -0700, enh wrote: >> >> On Sun, Apr 26, 2015 at 7:30 PM, Rich Felker <[email protected]> wrote: >> >> > On Sat, Apr 25, 2015 at 12:14:44PM -0700, enh wrote: >> >> >> what's the plan wrt SIGPIPE? the desktop is pretty inconsistent. many >> >> >> (but not all) commands install a signal handler that does _exit(0). >> >> >> others (coreutils 8.21's ls, say) do nothing. normally "what you do >> >> >> about SIGPIPE" isn't a problem but on Android that leads to a crash >> >> >> report and people filing "ls crashed" bugs against me. (our default >> >> >> shell PS setup is also noisy about crashes.) >> >> > >> >> > Why not just *block* SIGPIPE (with sigprocmask) so that the write >> >> > returns an error (EPIPE) and the program applies the same logic it >> >> > would for any other write error? >> >> >> >> toybox does a little better than toolbox there thanks to xwrite, but >> >> i've yet never met anyone who checks the return value of printf... >> >> >> >> plus there's the question of whether giving up because you're writing >> >> to a broken pipe is an error exit or not. you could add a special case >> >> to xwrite (and add xprintf and xputs and...), but since the whole idea >> >> is that code shouldn't have to care, it's easier just to install a >> >> signal handler that does _exit(0). >> > >> > _exit(0) is wrong and broken. It reports success when the command did >> > not succeed. >> >> coreutils seems divided on this issue. > > Could you provide some examples? I think POSIX is pretty clear that > you can't return success if the output was not successfully written. > As I already mentioned doing so results in data loss. I really doubt > coreutils is doing this, but well, GNU software is not always a good > example of doing the Right Thing...
i did in my original mail. >> > Failure of the caller to recognize that it didn't succeed >> > can result in data loss. If anything the right behavior for the signal >> > handler would be _exit(1) not _exit(0). But I think xwrite/xprintf >> > solves the issue more elegantly. Note that even if you don't check >> > every printf, you still get the error status from ferror and/or fflush >> > at close time (if you check them) but that might result in a lot of >> > wasted cpu time if you continue processing/writing after a pipe broke. >> >> it would also result in things like top(1) not exiting. > > If top is using stdio, it's easy to add a single ferror(stdout) check > to the main loop. If it's using write(), it _must_ be checking for > errors anyway since write can always return with a short/partial > write. But top is unlikely to be hooked up to a pipe or socket anyway; > it normally needs a terminal. the point is that then people need to think. if that were a plausible solution, this thread wouldn't exist. the advantage of the signal handler is that humans can keep on being humans. -- Elliott Hughes - http://who/enh - http://jessies.org/~enh/ Android native code/tools questions? Mail me/drop by/add me as a reviewer. _______________________________________________ Toybox mailing list [email protected] http://lists.landley.net/listinfo.cgi/toybox-landley.net
