[PATCH] better handling of fstab labels with devfs?

[Eric Sandeen <sandeen@xxxxxxx>]

As is well known at this point, if you turn on devfs but do not mount it
on /dev, mount-by-label will break.

This is a patch against the 2.4.21-kernel which puts the "old-style"
device names back into /proc/partitions _unless_ 

1) CONFIG_DEVFS_MOUNT is turned on, meaning devfs is mounted on /dev
   at boot time, or
2) the device major # is dynamically allocated by devfs (so, assume
   there is no "old" name available)

This still breaks in some corner cases, one that I can think of is if
the user does not mount devfs on /dev at boot time, but later does mount
it, then /proc/partitions will have old names in it, so they can't be
found -if- the user is also not running devfsd to get the old compat
names.

I'm not necessarily asking this to be applied upstream; I know it is not
a perfect solution, and maybe it doesn't make things much better.

But, I thought I'd throw it out there.  Does anyone see anything
horribly broken about the approach?

Thanks,

-Eric

===========================================================================
linux/fs/partitions/check.c
===========================================================================
 
--- /usr/tmp/TmpDir.11207-0/linux/fs/partitions/check.c_1.39    2003-07-21 
11:39:51.000000000 -0500
+++ linux/fs/partitions/check.c 2003-07-17 14:16:56.000000000 -0500
@@ -107,7 +107,14 @@
        unsigned int unit = (minor >> hd->minor_shift);
        unsigned int part = (minor & ((1 << hd->minor_shift) -1 ));
  
-       if ((unit < hd->nr_real) && hd->part[minor].de) {
+       /* Only show devfs names if devfs is mounted at boot time,
+        * or devfs owns this major.  Otherwise show old names.
+        */
+       if ((unit < hd->nr_real) && hd->part[minor].de
+#ifndef CONFIG_DEVFS_MOUNT
+           && devfs_owns_block_major(hd->major)
+#endif
+       ) {
                int pos;
  
                pos = devfs_generate_path (hd->part[minor].de, buf, 64);
 
===========================================================================
linux/fs/devfs/util.c
===========================================================================
 
--- /usr/tmp/TmpDir.11207-0/linux/fs/devfs/util.c_1.9   2003-07-21 
11:39:51.000000000 -0500
+++ linux/fs/devfs/util.c       2003-07-17 14:36:02.000000000 -0500
@@ -150,6 +150,16 @@
     0-3, 7-9, 11-63, 65-99, 101-113, 120-127, 199, 201, 240-255
     Total free: 122
 */
+
+/* pre-assigned majors */
+unsigned long assigned_major_list[] =
+    {INITIALISER64 (0xfffffb8f, 0xffffffff),  /*  Majors 0-31,    32-63    */
+     INITIALISER64 (0xfffffffe, 0xff03ffef),  /*  Majors 64-95,   96-127   */
+     INITIALISER64 (0x00000000, 0x00000000),  /*  Majors 128-159, 160-191  */
+     INITIALISER64 (0x00000280, 0xffff0000),  /*  Majors 192-223, 224-255  */
+    };
+
+/* currently allocated majors */
 static struct major_list block_major_list =
 {SPIN_LOCK_UNLOCKED,
     {INITIALISER64 (0xfffffb8f, 0xffffffff),  /*  Majors 0-31,    32-63    */
@@ -174,6 +184,22 @@
  
  
 /**
+ *     devfs_owns_block_major - Test whether a device nr is from devfs' pool
+ *     @major: The major number to test
+
+ *     Returns 1 if the major number is owned by devfs, 0 otherwise.
+ */
+
+int devfs_owns_block_major (int major)
+{
+    int devfs_major;
+
+    devfs_major = !test_bit (major, &assigned_major_list);
+    printk("major %d is %sowned by devfs (%d)\n", major, devfs_major ? "" : 
"not ", devfs_major);
+    return devfs_major;
+}   /*  End Function devfs_owns_block_major  */
+
+/**
  *     devfs_alloc_major - Allocate a major number.
  *     @type: The type of the major (DEVFS_SPECIAL_CHR or DEVFS_SPECIAL_BLK)
  
 
===========================================================================
linux/include/linux/devfs_fs_kernel.h
===========================================================================
 
--- /usr/tmp/TmpDir.11207-0/linux/include/linux/devfs_fs_kernel.h_1.9   
2003-07-21 11:39:51.000000000 -0500
+++ linux/include/linux/devfs_fs_kernel.h       2003-07-17 14:15:44.000000000 
-0500
@@ -107,6 +107,7 @@
                                   unsigned int flags, unsigned int major,
                                   unsigned int minor_start,
                                   umode_t mode, void *ops, void *info);
+extern int devfs_owns_block_major (int major);
 extern int devfs_alloc_major (char type);
 extern void devfs_dealloc_major (char type, int major);
 extern kdev_t devfs_alloc_devnum (char type);
@@ -276,6 +277,11 @@
     return;
 }
  
+static inline int devfs_owns_block_major (int major)
+{
+    return 0;
+}
+
 static inline int devfs_alloc_major (char type)
 {
     return -1;
 

-- 
Eric Sandeen      [C]XFS for Linux   http://oss.sgi.com/projects/xfs
sandeen@xxxxxxx   SGI, Inc.          651-683-3102