Re: src/stdio/__stdio_read.c

[Rich Felker <dalias@aerifal.cx>]

On Fri, Nov 16, 2012 at 10:29:36AM +0100, Szabolcs Nagy wrote:
> * Yuri Kozlov <yuray@komyakino.ru> [2012-11-16 11:40:57 +0400]:
> > size_t __stdio_read(FILE *f, unsigned char *buf, size_t len)
> > {
> > 	ssize_t cnt;
> > ...
> > 	cnt = syscall(SYS_readv, ...)
> > 
> > 	if (cnt <= 0) {
> > 		f->flags |= F_EOF ^ ((F_ERR^F_EOF) & cnt);
> > 		f->rpos = f->rend = 0;
> > 		return cnt;
> > 	}
> > ...
> > }
> > 
> > It not raise a problem when a signed value return as unsigned?
> > 
> 
> no, cnt is either 0 or -1 there (assuming readv works)
> 
> this is how __stdio_read is used (f->read):
> 
>         for (; l; l-=k, dest+=k) {
>                 k = __toread(f) ? 0 : f->read(f, dest, l);
>                 if (k+1<=1) {
>                         FUNLOCK(f);
>                         return (len-l)/size;
>                 }
>         }
> 
> it handles the k == -1 and k == 0 case

As far as I can tell, it would work just fine to have the f->read
function simply return 0 on both EOF and error; there do not seem to
be any callers that care to distinguish these cases. When I get around
to documenting stdio internals I might clean up some things like this.

Rich