Upgrade mdev to allow commands to be run on create/delete.

Both Jason Schoon and Giuseppe Ciotta deserve credit for this, I used elements
of both.  It's been upgraded so that you can specify that a given command
should run at create, at delete, or at both using different special characters
(@, $, and * respectively).  It uses the system() method of running command
lines which means you can use environment variables on the command line (it
sets $MDEV to the name of the current device being created/deleted, which is
useful if you matched it via regex), and the documentation warns that you need
a /bin/sh to make that work, so you probably want to pick a default shell.

1 files changed, 14 insertions, 8 deletions

diff --git a/include/usage.h b/include/usage.h
index 8defbd1fc..712eede63 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -1799,19 +1799,25 @@ USE_FEATURE_DATE_ISOFMT( \
         "\t-s\tScan /sys and populate /dev during system boot\n\n" \
         "Called with no options (via hotplug) it uses environment variables\n" \
         "to determine which device to add/remove."
-#ifdef CONFIG_FEATURE_MDEV_CONFIG
-#define mdev_notes_usage \
+#define mdev_notes_usage "" \
+USE_FEATURE_MDEV_CONFIG( \
         "The mdev config file contains lines that look like:\n" \
         "  hd[a-z][0-9]* 0:3 660\n\n" \
         "That's device name (with regex match), uid:gid, and permissions.\n\n" \
-        "Optionally, that can be followed (on the same line) by an asterisk\n" \
-        "and a command line to run after creating the corresponding device(s),\n"\
-        "ala:\n\n" \
-        "  hdc root:cdrom 660  *ln -s hdc cdrom\n\n" \
+        USE_FEATURE_MDEV_EXEC( \
+                "Optionally, that can be followed (on the same line) by a special character\n" \
+                "and a command line to run after creating/before deleting the corresponding\n" \
+                "device(s).  The environment variable $MDEV indicates the active device node\n" \
+                "(which is useful if it's a regex match).  For example:\n\n" \
+                "  hdc root:cdrom 660  *ln -s $MDEV cdrom\n\n" \
+                "The special characters are @ (run after creating), $ (run before deleting),\n" \
+                "and * (run both after creating and before deleting).  The commands run in\n" \
+                "the /dev directory, and use system() which calls /bin/sh.\n\n" \
+        ) \
         "Config file parsing stops on the first matching line.  If no config\n"\
         "entry is matched, devices are created with default 0:0 660.  (Make\n"\
-        "the last line match .* to override this.)\n\n"
-#endif
+        "the last line match .* to override this.)\n\n" \
+)
 
 #define mesg_trivial_usage \
         "[y|n]"