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| author | Dan Williams <dan.j.williams@intel.com> | 2008-04-21 10:51:07 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2008-07-21 21:54:40 -0700 |
| commit | e105b8bfc769b0545b6f0f395179d1e43cbee822 (patch) | |
| tree | 23a1f0839547829c4ca6e89cd40adf285eb9feb6 /Documentation | |
| parent | 93ded9b8fd42abe2c3607097963d8de6ad9117eb (diff) | |
| download | op-kernel-dev-e105b8bfc769b0545b6f0f395179d1e43cbee822.zip op-kernel-dev-e105b8bfc769b0545b6f0f395179d1e43cbee822.tar.gz | |
sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor
Why?:
There are occasions where userspace would like to access sysfs
attributes for a device but it may not know how sysfs has named the
device or the path. For example what is the sysfs path for
/dev/disk/by-id/ata-ST3160827AS_5MT004CK? With this change a call to
stat(2) returns the major:minor then userspace can see that
/sys/dev/block/8:32 links to /sys/block/sdc.
What are the alternatives?:
1/ Add an ioctl to return the path: Doable, but sysfs is meant to reduce
the need to proliferate ioctl interfaces into the kernel, so this
seems counter productive.
2/ Use udev to create these symlinks: Also doable, but it adds a
udev dependency to utilities that might be running in a limited
environment like an initramfs.
3/ Do a full-tree search of sysfs.
[kay.sievers@vrfy.org: fix duplicate registrations]
[kay.sievers@vrfy.org: cleanup suggestions]
Cc: Neil Brown <neilb@suse.de>
Cc: Tejun Heo <htejun@gmail.com>
Acked-by: Kay Sievers <kay.sievers@vrfy.org>
Reviewed-by: SL Baur <steve@xemacs.org>
Acked-by: Kay Sievers <kay.sievers@vrfy.org>
Acked-by: Mark Lord <lkml@rtr.ca>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-dev | 20 | ||||
| -rw-r--r-- | Documentation/filesystems/sysfs.txt | 6 |
2 files changed, 26 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-dev b/Documentation/ABI/testing/sysfs-dev new file mode 100644 index 0000000..a9f2b8b --- /dev/null +++ b/Documentation/ABI/testing/sysfs-dev @@ -0,0 +1,20 @@ +What: /sys/dev +Date: April 2008 +KernelVersion: 2.6.26 +Contact: Dan Williams <dan.j.williams@intel.com> +Description: The /sys/dev tree provides a method to look up the sysfs + path for a device using the information returned from + stat(2). There are two directories, 'block' and 'char', + beneath /sys/dev containing symbolic links with names of + the form "<major>:<minor>". These links point to the + corresponding sysfs path for the given device. + + Example: + $ readlink /sys/dev/block/8:32 + ../../block/sdc + + Entries in /sys/dev/char and /sys/dev/block will be + dynamically created and destroyed as devices enter and + leave the system. + +Users: mdadm <linux-raid@vger.kernel.org> diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt index 7f27b8f..9e9c348 100644 --- a/Documentation/filesystems/sysfs.txt +++ b/Documentation/filesystems/sysfs.txt @@ -248,6 +248,7 @@ The top level sysfs directory looks like: block/ bus/ class/ +dev/ devices/ firmware/ net/ @@ -274,6 +275,11 @@ fs/ contains a directory for some filesystems. Currently each filesystem wanting to export attributes must create its own hierarchy below fs/ (see ./fuse.txt for an example). +dev/ contains two directories char/ and block/. Inside these two +directories there are symlinks named <major>:<minor>. These symlinks +point to the sysfs directory for the given device. /sys/dev provides a +quick way to lookup the sysfs interface for a device from the result of +a stat(2) operation. More information can driver-model specific features can be found in Documentation/driver-model/. |
