Messages in this thread Patch in this message | | | Date | Tue, 18 Dec 2007 23:04:18 -0500 | From | Erez Zadok <> | Subject | [PATCH] XFS: don't expose sysv device encoding in inode->i_rdev |
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I did some testing on special-file copyup in unionfs, whereby unionfs calls vfs_mknod on a lower f/s to create (copyup) a device. The copyup functionality worked fine when unionfs was stacked on top of all file systems other than xfs. I found out that when I create a device with <maj,min> on xfs, then I stat(1) through the union, I get the sysv encoding of the <maj,min>.
The problem appears to be in the xfs_vn_mknod() function in xfs_iops.c: the code changes the rdev value using rdev = sysv_encode_dev(rdev); so it can fall through that case of the first switch statement in that function, and onto xfs_create(). Later in that function, however, it copies the sysv_encode'd rdev value into the inode that is going to be d_instantiate'd, thus exposing the sysv encoding to the VFS -- and to any stackable file system that may be using fsstack_copy_attr_all() to copy lower inode attributes to an upper inode.
The following small patch seems to fix the problem. Bug and fix were verified on v2.6.24-rc5-245-gc63a119. Someone with better understanding of XFS's internals should verify this patch.
Andrew, a related question: kdev_t.h defines several device <maj,min> encoding formats, which different file systems seems to use. Assuming that a file system can choose whatever internal encoding it wants, is there a uniform standard for what the VFS-level inode->i_rdev format should be? (vfs.txt is silent about the issue.)
Thanks, Erez.
XFS: don't expose internal sysv encoding to VFS inode->i_rdev
Signed:-off-by: Erez Zadok <ezk@cs.sunysb.edu>
diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c index 37e1167..daaa060 100644 --- a/fs/xfs/linux-2.6/xfs_iops.c +++ b/fs/xfs/linux-2.6/xfs_iops.c @@ -333,7 +333,8 @@ xfs_vn_mknod( ip = vn_to_inode(vp); if (S_ISCHR(mode) || S_ISBLK(mode)) - ip->i_rdev = rdev; + ip->i_rdev = MKDEV(sysv_major(rdev) & 0x1ff, + sysv_minor(rdev)); else if (S_ISDIR(mode)) xfs_validate_fields(ip); d_instantiate(dentry, ip);
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