Re: Read/write counts

[Theodore Tso <tytso@mit.edu>]

On Mon, Jun 04, 2007 at 11:02:23AM -0600, Matthew Wilcox wrote:
> On Mon, Jun 04, 2007 at 09:56:07AM -0700, Bryan Henderson wrote:
> > Programs that assume a full transfer are fairly common, but are 
> > universally regarded as either broken or just lazy, and when it does cause 
> > a problem, it is far more common to fix the application than the kernel.
> 
> Linus has explicitly forbidden short reads from being returned.  The
> original poster may get away with it for a specialised case, but for
> example, signals may not cause a return to userspace with a short read
> for exactly this reason.

Hmm, I'm not sure I would go that far.  Per the POSIX specification,
we support the optional BSD-style restartable system calls for signals
which will avoid short reads; but this is only true if SA_RESTART is
passed to sigaction().  Without SA_RESTART, we will indeed return
short reads, as required by POSIX.

I don't think Linus has said that short reads are always evil; I
certainly can't remember him ever making that statement.  Do you have
a pointer to a LKML message where he's said that?

							- Ted