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mdev: add large comment, fix a buglet with subsystem and /sys/block

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This commit is contained in:
Denis Vlasenko 2009-04-17 00:01:04 +00:00
parent 184f4ff432
commit 5ff9629b8f
1 changed files with 42 additions and 4 deletions
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46
util-linux/mdev.c
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@ -10,6 +10,41 @@
#include "libbb.h"
#include "xregex.h"
/* "mdev -s" scans /sys/class/xxx, looking for directories which have dev
* file (it is of the form "M:m\n"). Example: /sys/class/tty/tty0/dev
* contains "4:0\n". Directory name is taken as device name, path component
* directly after /sys/class/ as subsystem. In this example, "tty0" and "tty".
* Then mdev creates the /dev/device_name node.
*
* mdev w/o parameters is called as hotplug helper. It takes device
* and subsystem names from $DEVPATH and $SUBSYSTEM, extracts
* maj,min from "/sys/$DEVPATH/dev" and also examines
* $ACTION ("add"/"delete") and $FIRMWARE.
*
* If action is "add", mdev creates /dev/device_name similarly to mdev -s.
* (todo: explain "delete" and $FIRMWARE)
*
* If /etc/mdev.conf exists, it may modify /dev/device_name's properties.
* /etc/mdev.conf file format:
*
* [-][subsystem/]device user:grp mode [>|=path] [@|$|*command args...]
* [-]@maj,min[-min2] user:grp mode [>|=path] [@|$|*command args...]
*
* The device name or "subsystem/device" combo is matched against 1st field
* (which is a regex), or maj,min is matched against 1st field.
*
* Leading minus in 1st field means "don't stop on this line", otherwise
* search is stopped after the matching line is encountered.
*
* When line matches, the device node is created, chmod'ed and chown'ed.
* Then it moved to path, and if >path, a symlink to moved node is created
* Examples:
* =loop/ - moves to /dev/loop
* >disk/sda%1 - moves to /dev/disk/sdaN, makes /dev/sdaN a symlink
* Then "command args" is executed (via sh -c 'command args').
* @:execute on creation, $:on deletion, *:on both.
*/
struct globals {
int root_major, root_minor;
char *subsystem;
@ -96,8 +131,11 @@ static void make_device(char *path, int delete)
if (strstr(path, "/block/"))
type = S_IFBLK;
/* Make path point to subsystem/device_name */
path += sizeof("/sys/class/") - 1;
/* Make path point to "subsystem/device_name" */
if (path[5] == 'b') /* legacy /sys/block? */
path += sizeof("/sys/") - 1;
else
path += sizeof("/sys/class/") - 1;
#if !ENABLE_FEATURE_MDEV_CONF
mode = 0660;
@ -131,8 +169,8 @@ static void make_device(char *path, int delete)
keep_matching = ('-' == val[0]);
val += keep_matching; /* swallow leading dash */
/* Match against either subsystem/device_name
* or device_name alone */
/* Match against either "subsystem/device_name"
* or "device_name" alone */
name = strchr(val, '/') ? path : (char *) device_name;
/* Fields: regex uid:gid mode [alias] [cmd] */