GNU bug report logs - #18621
[BUG] wc -c incorrectly counts bytes in /sys

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Message #11 received at 18621 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: Pádraig Brady <P <at> draigbrady.com>
Cc: 18621 <at> debbugs.gnu.org, George Shuklin <george.shuklin <at> gmail.com>
Subject: Re: bug#18621: [BUG] wc -c incorrectly counts bytes in /sys
Date: Fri, 3 Oct 2014 11:26:34 -0700

On Fri, Oct 3, 2014 at 9:48 AM, Pádraig Brady <P <at> draigbrady.com> wrote:
> On 10/03/2014 03:47 PM, George Shuklin wrote:
...
> I'm not sure where the above code comes from,
> by coreutils trunk has the same behavior with these files.
> We could avoid it with the following patch.
> Note in the case where "real" small files don't
> take up space in the file system, this will involve a redundant read,
> however that will only be the case for small files so shouldn't
> be problematic.
>
> thanks,
> Pádraig.
>
> diff --git a/src/wc.c b/src/wc.c
> index 1ff007d..bf1ce76 100644
> --- a/src/wc.c
> +++ b/src/wc.c
> @@ -235,6 +235,7 @@ wc (int fd, char const *file_x, struct fstatus *fstatus)
>          fstatus->failed = fstat (fd, &fstatus->st);
>
>        if (! fstatus->failed && S_ISREG (fstatus->st.st_mode)
> +          && fstatus->st.st_blocks
>            && (current_pos = lseek (fd, 0, SEEK_CUR)) != -1
>            && (end_pos = lseek (fd, 0, SEEK_END)) != -1)
>          {

That looks like a fine fix.
However, a similar issue affects tac, when its lseek-SEEK_END fails:

  $ tac /sys/kernel/vmcoreinfo
  tac: /sys/kernel/vmcoreinfo: read error: Inappropriate ioctl for device

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