>On Sunday 06 July 2008 09:06:53 Vladimir Dronnikov wrote:
>> In particular /sys/block/loop* are the symlinks and mdev -s ceased to
>> mknod /dev/loop*.
To what exactly do these symlinks point? I have no access to a kernel later
than 2.6.24.
>
>Keep in mind that sysfs keeps changing. It has no stable API.
>So essentially it recurses into /sys/class/*/* (but no deeper), skips any
>nodes named "block" (because /sys/class/block didn't used to exist,
>so we can't rely on it being there and have to check /sys/block to find
>block devices, but now it's a symlink to the same place as /sys/block
>so if we _do_ find it it does not contain char devices).
>...The "symlink vs non-symlink" thing
>used to be a reliable and simple indicator of what was interesting.
>And then they changed the kernel again. They've broken mdev
>something like 5 times since the first shell script version, by changing
>sysfs to have a different (still undocumented) API...
That is when you stay within /sys/class or /sys/block. Operating on the
whole of /sys and following non-symlinks only will and does find all dev
files reliably (don't know about the above mentioned loop devices).
There is one assumption: a node name and respective dev file contents are
distinct for all non-symlink paths within /sys.
Being that sysfs continually evolves and imho busybox should work on many
kernels, I have proposed and submitted a patch for mdev that evades the
sysfs/kernel version specific problem.
For convenience, I have attached the patch to this post.
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Index: util-linux/mdev.c
===================================================================
--- util-linux/mdev.c (revision 22793)
+++ util-linux/mdev.c (working copy)
@@ -19,9 +19,6 @@
#define root_major (G.root_major)
#define root_minor (G.root_minor)
-/* Prevent infinite loops in /sys symlinks */
-#define MAX_SYSFS_DEPTH 3
-
/* We use additional 64+ bytes in make_device() */
#define SCRATCH_SIZE 80
@@ -75,11 +72,10 @@
* "/sys/block/..." is for block devices. "/sys/bus" etc is not!
* Since kernel 2.6.25 block devices are also in /sys/class/block. */
/* TODO: would it be acceptable to just use strstr(path, "/block/")? */
- if (strncmp(&path[5], "class/block/"+6, 6) != 0
- && strncmp(&path[5], "class/block/", 12) != 0)
- type = S_IFCHR;
- else
- type = S_IFBLK;
+ if (NULL == strstr(&path[4], "/block/"))
+ type = S_IFCHR;
+ else
+ type = S_IFBLK;
if (ENABLE_FEATURE_MDEV_CONF) {
FILE *fp;
@@ -319,15 +315,6 @@
return TRUE;
}
-/* Directory callback for /sys/ traversal */
-static int FAST_FUNC dirAction(const char *fileName UNUSED_PARAM,
- struct stat *statbuf UNUSED_PARAM,
- void *userData UNUSED_PARAM,
- int depth)
-{
- return (depth >= MAX_SYSFS_DEPTH ? SKIP : TRUE);
-}
-
/* For the full gory details, see linux/Documentation/firmware_class/README
*
* Firmware loading works like this:
@@ -420,17 +407,8 @@
root_major = major(st.st_dev);
root_minor = minor(st.st_dev);
- /* ACTION_FOLLOWLINKS is needed since in newer kernels
- * /sys/block/loop* (for example) are symlinks to dirs,
- * not real directories.
- * (kernel's CONFIG_SYSFS_DEPRECATED makes them real dirs,
- * but we can't enforce that on users) */
- recursive_action("/sys/block",
- ACTION_RECURSE | ACTION_FOLLOWLINKS,
- fileAction, dirAction, temp, 0);
- recursive_action("/sys/class",
- ACTION_RECURSE | ACTION_FOLLOWLINKS,
- fileAction, dirAction, temp, 0);
+ recursive_action("/sys", ACTION_RECURSE
+ fileAction, NULL, temp, 0);
} else {
/* Hotplug:
* env ACTION=... DEVPATH=... mdev
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