read() builtin doesn't read integer value /proc files (but bash's does)

[Steve Schnepp <steve.schnepp@xxxxxxxxx>]

Hi, I opened bug 595063 on the debian BTS [1] and I was suggested to
resend the email upstream.

So I copied the body of the bug below :

dash's read() builtin seems to read the underlying file 1 char at a
time. This doesn't work with some files under /proc, since procfs isn't
fully POSIX compliant.

With bash it works :

$ bash -c 'read MAX < /proc/sys/kernel/pid_max; echo $MAX'
32768

With dash it only reads the first character :

$ dash -c 'read MAX < /proc/sys/kernel/pid_max; echo $MAX'
3

If we use the cat(1) external program it works :

$ dash -c 'MAX=$(cat /proc/sys/kernel/pid_max); echo $MAX'
32768

After a little digging, it only appears on files that contains just an
integer value. When asked to read with a non-null offset (*ppos != 0),
__do_proc_dointvec() just returns 0 (meaning an EOF) as shown on [2].

I'm aware that the issue isn't strictly a dash one, since it has the
right to read one character at a time. But since fixing procfs to be
conforming to POSIX isn't a realistic option, would it be possible to
have a workaround that doesn't involve an external tool like cat(1) ?

[1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=595063
[2] http://lxr.linux.no/#linux+v2.6.32/kernel/sysctl.c#L2371
--
Steve Schnepp
http://blog.pwkf.org/
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