linux-kernel - Re: [PATCH] x86_64: fix delayed signals

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Message-ID: <alpine.LFD.1.10.0807111110330.2936@woody.linux-foundation.org>
Date:	Fri, 11 Jul 2008 11:16:40 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Roland McGrath <roland@...hat.com>
cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Elias Oltmanns <eo@...ensachen.de>,
	Török Edwin <edwintorok@...il.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] x86_64: fix delayed signals



On Fri, 11 Jul 2008, Roland McGrath wrote:
>
> > +		/* Only check signals if we have filled at least one entry! */
> > +		if (signal_pending(current))
> > +			return -EINTR;
> 
> Shouldn't it return the short count?  
> (And if not, then probably should be -ERESTARTSYS.)

readdir (getdents) is a complex system call, and the path is

    sys_getdents64() ->
      vfs_readdir (with 'filldir64' as a callback) ->
        low-level filesystem 'readdir' function ->	
          filldir64 callback

and what happens is that when that 'filldir64()' callback returns an 
error, the low-level filesystem just stops and returns with a success 
(because everything worked for _it_ - it was the callback that errored 
out).

The 'sys_getdents64()' then does:

	..
	lastdirent = buf.previous;
        if (lastdirent) {
                typeof(lastdirent->d_off) d_off = file->f_pos;
                error = -EFAULT;
                if (__put_user(d_off, &lastdirent->d_off))
                        goto out_putf;
                error = count - buf.count;
        }
	..

ie we'll do that "return partial buffer size" at that level, not deep in 
the callback.

So making the callback just return an error is the right thing to do - 
because the callers will then fix up the file offset in the last directory 
entry and the final return value.

			Linus
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