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linux-yocto/Documentation/ABI/testing/sysfs-dev
Dan Williams e105b8bfc7 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>
2008-07-21 21:54:40 -07:00

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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 ":". 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