[PATCH] tail can't handle the /proc directory

[Kazuo TAKADA]

Hi,

I found bug in busybox 1.7.2 and before.
The tail command can't handle the /proc directory and doesn't return
from a while loop.

For example:
----------------------------------------
% ./busybox tail /proc/meminfo
(It doesn't exit...)
----------------------------------------

The patch below can resolve this problem.

----------------------------------------------------------------------
--- coreutils/tail.c.orig	2007-09-03 20:48:40.000000000 +0900
+++ coreutils/tail.c	2007-10-02 17:54:34.000000000 +0900
@@ -51,7 +51,7 @@
 	struct stat sbuf;
 
 	end = current = lseek(fd, 0, SEEK_CUR);
-	if (!fstat(fd, &sbuf))
+	if (!fstat(fd, &sbuf) && sbuf.st_size)
 		end = sbuf.st_size;
 	lseek(fd, end < current ? 0 : current, SEEK_SET);
 	r = safe_read(fd, buf, count);
----------------------------------------------------------------------

'man fstat' said:

    >Linux Notes
      :
    > For most files under the /proc directory, stat() does not return the
    > file size in the st_size field; instead the field is returned with
    > the value 0.

Therefore, fstat() returns 0(=SUCCESS) and sbuf.st_size is set with
value 0. As a result, 'end' becomes 0 and lseek(fd, 0, SEEK_SET) is
executed over and over again.


Best regards,
Kazuo TAKADA