Commit f598f82e authored Jan 24, 2017 by Coly Li Committed by Linus Torvalds Jan 24, 2017

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

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: Coly Li <colyli@suse.de>
Reported-by: Nong Li <nongli1031@gmail.com>
Tested-by: Nong Li <nongli1031@gmail.com>
Cc: Richard Weinberger <richard.weinberger@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 4180c4c1

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)

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