linux-kernel - [PATCH] APM: fix type of secsize in mac.c

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Date:	Thu, 18 Dec 2014 15:51:14 +0000
From:	Alexander Kim <Alexander.Kim@...agon-software.com>
To:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"axboe@...nel.dk" <axboe@...nel.dk>
CC:	Alexey Adadurov <Alexey.Adadurov@...agon-software.com>
Subject: [PATCH] APM: fix type of secsize in mac.c

Hi all
Our company had been working on a project for a customer and faced the following problem:

One line summary of the problem: 
                Kernel detects wrong partitions sizes for large volume with APM partition
                table.

Full description of the problem/report:
                When using 2+ TB volume with APM partition table and one of the partitions
                on it (also may be single partition) of size 2+ TB, one can notice that
                (for example block device is sdb)
                '/sys/block/sdb/size' contains significantly different (with factor greater
                than 2) size than the sum of all '/sys/block/sdb/sdb*/size'  

                The problem is in block/partitions/mac.c source: 
                in function
                int mac_partition(struct parsed_partitions *state)
                the declaration of 'secsize' variable is 'unsigned secsize', but should be
                'sector_t secsize'

Keywords:
                APM, kernel, block, mac, sector_t, secsize

All significant environment information you could find in attachments (env.txt). The bug also appears in the latest upstream kernel:
http://lxr.free-electrons.com/source/block/partitions/mac.c#L35

A small shell script or example program which triggers the problem
                Bug could be reproduced by two shell commands:
                               i=0; for f in /sys/block/sdb/sdb*/size; do let i=$i+`cat $f`; done; echo
                               $i
                               cat /sys/block/sdb/size
                The result is two significantly different numbers.

Simple fix:  replace 'unsigned secsize' with 'sector_t secsize' (*.patch in
attachements) in block/partition/mac.c

Download attachment "APM_secsize_type.patch" of type "application/octet-stream" (510 bytes)

View attachment "env.txt" of type "text/plain" (77632 bytes)