Re: [PATCH 1/2] libmtd: Add support to access OOB available size

[xiaolei li <xiaolei.li-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>]

On Mon, 2018-04-09 at 10:37 +0200, Boris Brezillon wrote:
> On Mon, 9 Apr 2018 16:33:11 +0800
> xiaolei li <xiaolei.li-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org> wrote:
> 
> > Hi Boris,
> > 
> > On Mon, 2018-04-09 at 09:35 +0200, Boris Brezillon wrote:
> > > On Mon, 9 Apr 2018 15:25:39 +0800
> > > xiaolei li <xiaolei.li-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org> wrote:
> > >   
> > > > Hi David,
> > > > 
> > > > On Mon, 2018-04-09 at 08:58 +0200, David Oberhollenzer wrote:  
> > > > > Hi,
> > > > > 
> > > > > On 04/09/2018 05:10 AM, Xiaolei Li wrote:    
> > > > > > @@ -769,6 +774,8 @@ int mtd_get_dev_info1(libmtd_t desc, int mtd_num, struct mtd_dev_info *mtd)
> > > > > >  		return -1;
> > > > > >  	if (dev_read_pos_int(lib->mtd_oob_size, mtd_num, &mtd->oob_size))
> > > > > >  		return -1;
> > > > > > +	if (dev_read_pos_int(lib->mtd_oobavail, mtd_num, &mtd->oobavail))
> > > > > > +		return -1;
> > > > > >  	if (dev_read_pos_int(lib->mtd_region_cnt, mtd_num, &mtd->region_cnt))
> > > > > >  		return -1;
> > > > > >  	if (dev_read_hex_int(lib->mtd_flags, mtd_num, &ret))    
> > > > > 
> > > > > I'm not sure if it is a good idea to do a hard fail here, since this
> > > > > depends on a recent change to the kernel.
> > > > > 
> > > > > It might be preferable to catch and handle ENOENT, otherwise the next
> > > > > release of mtd-utils will only work on the next kernel release onward.
> > > > >     
> > > > Yes, it is. The hard fail return here seems not good.
> > > >   
> > > > > Maybe mtd_oobavail could to be set to some reasonable default that
> > > > > retains the current behaviour on "older" kernels?
> > > > >     
> > > > What about setting 0 as default?  
> > > 
> > > I didn't look closely at the code yet, but shouldn't we do something
> > > like:
> > > 
> > > 1/ search for oobavail file in sysfs
> > > 2/ if it's not there use the GETOOBSEL or GETECCLAYOUT ioctl to get
> > >    this information  
> > MEMGETOOBSEL and GETECCLAYOUT are obsoleted. Should we keep using them
> > here?
> 
> Yes we should, otherwise old kernels won't work with new versions of
> mtd-utils.
OK.

@David, do you have other comments? If no, I will work for next patch to
add GETOOBSEL/GETECCLAYOUT ioctl support as Boris's suggestion.