linux-kernel - Re: [PATCH 1/1] tools: iio: fix iio_generic

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Message-ID: <ZZrRRNTUbXaDIgRU@sunspire>
Date: Sun, 7 Jan 2024 18:28:52 +0200
From: Petre Rodan <petre.rodan@...dimension.ro>
To: Jonathan Cameron <jic23@...nel.org>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH 1/1] tools: iio: fix iio_generic_buffer


Hi Jonathan,

On Sun, Jan 07, 2024 at 03:53:33PM +0000, Jonathan Cameron wrote:
> On Thu,  4 Jan 2024 12:12:45 +0200
> Petre Rodan <petre.rodan@...dimension.ro> wrote:
> 
> > Fix code flow problem and floating point exception caused by improper
> > directory stream positioning.
> > 
> > Fixes: <e58537ccce733> ("staging: iio: update example application.")
> > Signed-off-by: Petre Rodan <petre.rodan@...dimension.ro>
> Hi Petre,
> 
> This doesn't really explain 'why' seeekdir(dp, 0) is wrong.
> My assumption is that telldir() would not have returned 0 on this particular
> system?  Could you confirm that and update the message to explain why
> seekdir(dp, 0) is not equivalent to rewinddir(dp).

it looks like there is a 32-bit specific bug in one of the glibc patches that
the stable Gentoo Linux is using [1]. telldir returns (u32)(-1) if seekdir is
used which ends up in a floating point exception.

it so happens that the rewinddir() function (which is equivalent) works
correctly. so it is a fix for Gentoo users and should not impact anyone else.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=31212

my very best regards,
peter

> Thanks,
> 
> Jonathan
> 
> > ---
> >  tools/iio/iio_utils.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/iio/iio_utils.c b/tools/iio/iio_utils.c
> > index 6a00a6eecaef..c5c5082cb24e 100644
> > --- a/tools/iio/iio_utils.c
> > +++ b/tools/iio/iio_utils.c
> > @@ -376,7 +376,7 @@ int build_channel_array(const char *device_dir, int buffer_idx,
> >  		goto error_close_dir;
> >  	}
> > 
> > -	seekdir(dp, 0);
> > +	rewinddir(dp);
> >  	while (ent = readdir(dp), ent) {
> >  		if (strcmp(ent->d_name + strlen(ent->d_name) - strlen("_en"),
> >  			   "_en") == 0) {
> > --
> > 2.41.0

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