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From: Szabolcs Nagy <nsz@port70.net>
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Subject: Re: src/stdio/__stdio_read.c
Date: Fri, 16 Nov 2012 10:29:36 +0100
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* 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