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bug#19969: problem: wc -c doesn't read actual # of bytes in file

From: Eric Blake
Subject: bug#19969: problem: wc -c doesn't read actual # of bytes in file
Date: Mon, 02 Mar 2015 06:57:02 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 02/28/2015 01:59 AM, Linda Walsh wrote:
> (coreutils-8.21-7.7.7)
> wc -c(bytes) doesn't seem to reliably read the number
> of bytes in a file.
> I was wanting to find out what the largest data-source
> files in '/proc' and '/sys' (didn't get around to trying
> /sys, since all the files under /proc/sys return 0 bytes.

The Linux kernel is notoriously bad about advertising 0-length file size
for non-empty contents of files within sysfs and procfs.  Any program
that trusts just stat() output will report 0; the only way to see
non-zero sizes on these special files is to open() and read() them (I'm
not even sure if lseek(SEEK_END) does the trick) - but fixing that is
something for the kernel folks to do, and not coreutils to work around,
because it is more than coreutils that is affected by the kernel's lies.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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