Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 013bbbc3 authored by Coly Li's avatar Coly Li Committed by Greg Kroah-Hartman
Browse files

romfs: use different way to generate fsid for BLOCK or MTD 


[ Upstream commit f598f82e204ec0b17797caaf1b0311c52d43fb9a ]

Commit 8a59f5d2 ("fs/romfs: return f_fsid for statfs(2)") generates
a 64bit id from sb->s_bdev->bd_dev.  This is only correct when romfs is
defined with CONFIG_ROMFS_ON_BLOCK.  If romfs is only defined with
CONFIG_ROMFS_ON_MTD, sb->s_bdev is NULL, referencing sb->s_bdev->bd_dev
will triger an oops.

Richard Weinberger points out that when CONFIG_ROMFS_BACKED_BY_BOTH=y,
both CONFIG_ROMFS_ON_BLOCK and CONFIG_ROMFS_ON_MTD are defined.
Therefore when calling huge_encode_dev() to generate a 64bit id, I use
the follow order to choose parameter,

- CONFIG_ROMFS_ON_BLOCK defined
  use sb->s_bdev->bd_dev
- CONFIG_ROMFS_ON_BLOCK undefined and CONFIG_ROMFS_ON_MTD defined
  use sb->s_dev when,
- both CONFIG_ROMFS_ON_BLOCK and CONFIG_ROMFS_ON_MTD undefined
  leave id as 0

When CONFIG_ROMFS_ON_MTD is defined and sb->s_mtd is not NULL, sb->s_dev
is set to a device ID generated by MTD_BLOCK_MAJOR and mtd index,
otherwise sb->s_dev is 0.

This is a try-best effort to generate a uniq file system ID, if all the
above conditions are not meet, f_fsid of this romfs instance will be 0.
Generally only one romfs can be built on single MTD block device, this
method is enough to identify multiple romfs instances in a computer.

Link: http://lkml.kernel.org/r/1482928596-115155-1-git-send-email-colyli@suse.de


Signed-off-by: default avatarColy Li <colyli@suse.de>
Reported-by: default avatarNong Li <nongli1031@gmail.com>
Tested-by: default avatarNong Li <nongli1031@gmail.com>
Cc: Richard Weinberger <richard.weinberger@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarSasha Levin <alexander.levin@verizon.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 093d494c

fs/romfs/super.c

+22 −1
Original line number Diff line number Diff line
@@ -74,6 +74,7 @@ 
#include <linux/highmem.h>

#include <linux/pagemap.h>

#include <linux/uaccess.h>

#include <linux/major.h>

#include "internal.h"



static struct kmem_cache *romfs_inode_cachep;
@@ -416,7 +417,22 @@ static void romfs_destroy_inode(struct inode *inode) 
static int romfs_statfs(struct dentry *dentry, struct kstatfs *buf)

{

	struct super_block *sb = dentry->d_sb;

	u64 id = huge_encode_dev(sb->s_bdev->bd_dev);

	u64 id = 0;



	/* When calling huge_encode_dev(),

	 * use sb->s_bdev->bd_dev when,

	 *   - CONFIG_ROMFS_ON_BLOCK defined

	 * use sb->s_dev when,

	 *   - CONFIG_ROMFS_ON_BLOCK undefined and

	 *   - CONFIG_ROMFS_ON_MTD defined

	 * leave id as 0 when,

	 *   - CONFIG_ROMFS_ON_BLOCK undefined and

	 *   - CONFIG_ROMFS_ON_MTD undefined

	 */

	if (sb->s_bdev)

		id = huge_encode_dev(sb->s_bdev->bd_dev);

	else if (sb->s_dev)

		id = huge_encode_dev(sb->s_dev);



	buf->f_type = ROMFS_MAGIC;

	buf->f_namelen = ROMFS_MAXFN;
@@ -489,6 +505,11 @@ static int romfs_fill_super(struct super_block *sb, void *data, int silent) 
	sb->s_flags |= MS_RDONLY | MS_NOATIME;

	sb->s_op = &romfs_super_ops;



#ifdef CONFIG_ROMFS_ON_MTD

	/* Use same dev ID from the underlying mtdblock device */

	if (sb->s_mtd)

		sb->s_dev = MKDEV(MTD_BLOCK_MAJOR, sb->s_mtd->index);

#endif

	/* read the image superblock and check it */

	rsb = kmalloc(512, GFP_KERNEL);

	if (!rsb)