Re: gzio/http problem

[Stefan Fritsch]

On Fri, 29 Apr 2016, Andrei Borzenkov wrote:

> 29.04.2016 00:54, Vladimir 'phcoder' Serbinenko пишет:
> > HTTP code should never return short reads. The whole subsystem relies on
> > never having short reads from any fs or network driver
> > 
> 
> HTTP code never returns short reads itself. But it sets EOF on socket in
> case something bad happens, and in this case we return currently
> received data to caller in net core.
> 
>       if (!net->eof)
>         {
>           try++;
>           grub_net_poll_cards (GRUB_NET_INTERVAL +
>                                (try * GRUB_NET_INTERVAL_ADDITION),
> &net->stall);
>         }
>       else
>         return total;
> 
> Disallowing short reads means also we should also disallow files with
> unknown size. I think that's unrealistic.

I think I have found the problem:

http_seek() creates a new connection but does not reset the eof flag. 
grub_net_fs_read_real() then does a short read because of the set eof 
flag.


This patch seems to fix the issue:

@@ -453,6 +461,7 @@ http_seek (struct grub_file *file, grub_off_t off)
     }
 
   file->device->net->stall = 0;
+  file->device->net->eof = 0;
   file->device->net->offset = off;
 
   data = grub_zalloc (sizeof (*data));


Though one could also argue that grub_net_seek_real() should reset the eof 
flag before calling file->device->net->protocol->seek().


Cheers,
Stefan