On 07/07/2014 11:00 AM, Naoya Horiguchi wrote:
> +.SH RETURN VALUE
> +On success,
> +.BR fincore ()
> +returns 0.
> +On error, \-1 is returned, and
> +.I errno
> +is set appropriately.
Is this accurate? From reading the syscall itself, it looked like it
did this:
> + * Return value is the number of pages whose data is stored in fc->buffer.
> + */
> +static long do_fincore(struct fincore_control *fc, int nr_pages)
and:
> +SYSCALL_DEFINE6(fincore, int, fd, loff_t, start, long, nr_pages,
...
> + while (fc.nr_pages > 0) {
> + memset(fc.buffer, 0, fc.buffer_size);
> + ret = do_fincore(&fc, min(step, fc.nr_pages));
> + /* Reached the end of the file */
> + if (ret == 0)
> + break;
> + if (ret < 0)
> + break;
...
> + }
...
> + return ret;
> +}
Which seems that for a given loop of do_fincore(), you might end up
returning the result of that *single* iteration of do_fincore() instead
of the aggregate of the entire syscall.
So, it can return <0 on failure, 0 on success, or also an essentially
random >0 number on success too.
Why not just use the return value for something useful instead of
hacking in the extras->nr_entries stuff? Oh, and what if that
> + if (extra)
> + __put_user(nr, &extra->nr_entries);
fails? It seems like we might silently forget to tell userspace how
many entries we filled.
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