Current git tree broke busybox start-stop-daemon

[Joakim Tjernlund]

> -----Original Message-----
> From: Alexey Dobriyan [mailto:adobriyan at gmail.com]
> Sent: den 16 april 2008 21:47
> To: Al Viro
> Cc: Joakim Tjernlund; linux-kernel at vger.kernel.org; ebiederm at xmission.com
> Subject: Re: Current git tree broke busybox start-stop-daemon
> 
> On Wed, Apr 16, 2008 at 08:34:17PM +0100, Al Viro wrote:
> > On Wed, Apr 16, 2008 at 11:00:57PM +0400, Alexey Dobriyan wrote:
> > > On Wed, Apr 16, 2008 at 07:25:02PM +0200, Joakim Tjernlund wrote:
> > > > open("/proc/1/stat", O_RDONLY|O_LARGEFILE) = 4
> > > > _llseek(4, 0, 0xbfb94898, SEEK_END)     = -1 EINVAL (Invalid argument)
> > >
> > > > So it appears that lseek is no longer allowed for /proc/1/stat
> > > > Bug or feature?
> > > > start-stop-daemon works fine in 2.6.23
> > >
> > > That's what happens when switching ->llseek method from NULL
> > > (effectively, default_llseek), to seq_lseek (which rejects SEEK_END).
> > >
> > > commit be614086a4aff163d5aa0dc160638d1193b59cde
> > > commit ee992744ea53db0a90c986fd0a70fbbf91e7f8bd
> > >
> > > Al, do you remember why SEEK_END was omitted back then?
> >
> > Because there's no sane way to implement it?
> 
> Ugly ->index games, sigh...
> 
> > Note that original cheerfully
> > did nothing, since it had zero ->i_size for that file.  Which makes program
> > in question very odd - what behaviour does it rely upon?
> 
> Busybox just wants to estimate size of a file. And it knows about
> zero-length /proc/*/stat .
> 
> libbb/read.c:
> 
> void *xmalloc_open_read_close(const char *filename, size_t *sizep)
> {
> 	char *buf;
> 	size_t size = sizep ? *sizep : INT_MAX;
> 	int fd;
> 	off_t len;
> 
> 	fd = xopen(filename, O_RDONLY);
> 	/* /proc/N/stat files report len 0 here */
> 	/* In order to make such files readable, we add small const */
> 	len = xlseek(fd, 0, SEEK_END) | 0x3ff; /* + up to 1k */
> 		...

So maybe bb should change to fstat() instead? But it would be nice if
you could restore the old behavior for one or two releases so bb has a can
catch up.

   Jocke