[PATCH] prevent retries on fclose/fflush after write errors

[Mike Frysinger]

On Tuesday 13 March 2012 02:06:10 Rich Felker wrote:
> On Tue, Mar 13, 2012 at 01:43:36AM -0400, Mike Frysinger wrote:
> > On Sunday 11 March 2012 20:50:27 Denys Vlasenko wrote:
> > > On Sunday 11 March 2012 18:10, Rich Felker wrote:
> > > > On Sun, Mar 11, 2012 at 04:12:19PM +0100, Denys Vlasenko wrote:
> > > > > On Sunday 11 March 2012 14:46, Denys Vlasenko wrote:
> > > > > > I propose the following patch.
> > > > > > Only compile tested by me, care to run-test?
> > > > > 
> > > > > A more correct (I hope) version:
> > > > I'm curious why this is such a big patch introducing new functions
> > > > and struct members. Couldn't it be just a one-line change in the
> > > > function that writes out the buffers (i.e. do the buffer-voiding as
> > > > soon as the error is hit rather than testing for it later)?
> > > 
> > > EINTR and EAGAIN should not result in output buffers being dropped.
> > > You need to remember the error code for this.
> > 
> > should not, but fairly certain POSIX allows us to.  i'd note that glibc
> > handles EINTR/EAGAIN in their fwrite/fread loops so that higher code
> > doesn't have to write "safe_fwrite" like they do with "safe_read". 
> > would be nice if uClibc could provide this too if it's not too much
> > overhead.
> 
> Looping in fread/fwrite when EINTR/EAGAIN is encountered is definitely
> wrong and harmful behavior. If the application has installed an
> interrupting signal handler, the intent is to allow the signal to
> break out of blocked IO operations. And likewise if the file
> descriptor is in nonblocking mode, the idea is that the application
> would rather get an error than block. Since POSIX specifies these
> errors for fgetc/fputc (and thereby for all stdio functions defined in
> terms of these two), I think it's clearly wrong for an implementation
> to hide them behind retry loops.

i read through the glibc code and the manual and couldn't find specific handling 
of these errnos, so i'm probably just misremembering

we already provide the helper TEMP_FAILURE_RETRY() for people who want this, 
so that should be sufficient for those who want to opt in to that behavior.
-mike
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