From e105b8bfc769b0545b6f0f395179d1e43cbee822 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Mon, 21 Apr 2008 10:51:07 -0700 Subject: 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 Cc: Tejun Heo Acked-by: Kay Sievers Reviewed-by: SL Baur Acked-by: Kay Sievers Acked-by: Mark Lord Acked-by: H. Peter Anvin Signed-off-by: Dan Williams Signed-off-by: Greg Kroah-Hartman --- Documentation/ABI/testing/sysfs-dev | 20 ++++++++++++++++++++ Documentation/filesystems/sysfs.txt | 6 ++++++ 2 files changed, 26 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-dev (limited to 'Documentation') diff --git a/Documentation/ABI/testing/sysfs-dev b/Documentation/ABI/testing/sysfs-dev new file mode 100644 index 000000000000..a9f2b8b0530f --- /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 +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 ":". 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 diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt index 7f27b8f840d0..9e9c348275a9 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 :. 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/. -- cgit v1.2.3