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Subject: [PATCH] /dev/mem: Allow rewinding
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Dave Jones <davej@redhat.com>, Andrew Morton <akpm@linux-foundation.org>,
       Wu Fengguang <fengguang.wu@intel.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
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Date: Mon, 05 Apr 2010 23:19:05 +0200
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Le lundi 05 avril 2010 à 23:04 +0200, Eric Dumazet a écrit :
> Andrew, commit dcefafb6ac90ece8d68a6c203105f3d313e52da4 seems to be the
> problem. 
> 
> It breaks rewinds (negative offsets to lseek (... SEEK_CUR))
> 

Here is a patch to make rewind working again on /dev/mem

[PATCH] /dev/mem: Allow rewinding

commit dcefafb6 (/dev/mem: dont allow seek to last page)
inadvertently disabled rewinding on /dev/mem.

This broke x86info for example.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 1f3215a..3973a1d 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -710,11 +710,6 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
 	switch (orig) {
 	case SEEK_CUR:
 		offset += file->f_pos;
-		if ((unsigned long long)offset <
-		    (unsigned long long)file->f_pos) {
-			ret = -EOVERFLOW;
-			break;
-		}
 	case SEEK_SET:
 		/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
 		if ((unsigned long long)offset >= ~0xFFFULL) {