Merge branch 'merge' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc

[safe/jmp/linux-2.6] / Documentation / filesystems / sysfs.txt

diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt
index 89b1d19..9e9c348 100644 (file)
--- a/Documentation/filesystems/sysfs.txt
+++ b/Documentation/filesystems/sysfs.txt
@@ -51,7 +51,7 @@ for the attributes, providing a means to read and write kernel
 attributes.
 
 Attributes should be ASCII text files, preferably with only one value
-per file. It is noted that it may not be efficient to contain only
+per file. It is noted that it may not be efficient to contain only one
 value per file, so it is socially acceptable to express an array of
 values of the same type. 
 
@@ -176,8 +176,10 @@ implementations:
   Recall that an attribute should only be exporting one value, or an
   array of similar values, so this shouldn't be that expensive. 
 
-  This allows userspace to do partial reads and seeks arbitrarily over
-  the entire file at will. 
+  This allows userspace to do partial reads and forward seeks
+  arbitrarily over the entire file at will. If userspace seeks back to
+  zero or does a pread(2) with an offset of '0' the show() method will
+  be called again, rearmed, to fill the buffer.
 
 - On write(2), sysfs expects the entire buffer to be passed during the
   first write. Sysfs then passes the entire buffer to the store()
@@ -192,6 +194,9 @@ implementations:
 
 Other notes:
 
+- Writing causes the show() method to be rearmed regardless of current
+  file position.
+
 - The buffer will always be PAGE_SIZE bytes in length. On i386, this
   is 4096. 
 
@@ -238,11 +243,12 @@ Top Level Directory Layout
 The sysfs directory arrangement exposes the relationship of kernel
 data structures. 
 
-The top level sysfs diretory looks like:
+The top level sysfs directory looks like:
 
 block/
 bus/
 class/
+dev/
 devices/
 firmware/
 net/
@@ -269,6 +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/.