I'm working with JBODs and would like to access the disks inside through
dm-multipath. For performance reasons I would like to use to prioritizer
to pin individual disks to different paths. For testing purposes this
can be done with the weighted_path prioritizer, but for production use
this is unsatisfactory, as neither the device name nor the SCSI address
are persistent over reboots. Thus I wrote a new, simple prioritizer to
call an external program to determine what the prio should be. I would
like to ask if there is interest to include this (or something similar)
upstream (see attached patch).
Remark: After I did this, I've seen the wwn regex mode in the upcoming
0.6 version, which would also provide a solution to the problem I
started out with. But using this would still means one had to recreate
multipath.conf each time one replaces a failed disk, so I still believe
having an external upcall makes sense in some situations.
Any thoughts?
From 124b54531dd1859755175ca5e9e4882d15cdd87d Mon Sep 17 00:00:00 2001
From: Oliver Mangold <oliver.mangold@xxxxxxxxxxxx>
Date: Fri, 22 Apr 2016 12:53:55 +0200
Subject: [PATCH] libmultipath: adding new prioritizer 'upcall' to call
external program
---
libmultipath/prioritizers/Makefile | 1 +
libmultipath/prioritizers/upcall.c | 25 +++++++++++++++++++++++++
multipath/multipath.conf.5 | 6 ++++++
3 files changed, 32 insertions(+)
create mode 100644 libmultipath/prioritizers/upcall.c
diff --git a/libmultipath/prioritizers/Makefile b/libmultipath/prioritizers/Makefile
index 6cfac88..1b32d00 100644
--- a/libmultipath/prioritizers/Makefile
+++ b/libmultipath/prioritizers/Makefile
@@ -15,6 +15,7 @@ LIBS = \
libpriodatacore.so \
libpriohds.so \
libprioweightedpath.so \
+ libprioupcall.so \
libprioiet.so
CFLAGS += -I..
diff --git a/libmultipath/prioritizers/upcall.c b/libmultipath/prioritizers/upcall.c
new file mode 100644
index 0000000..175b8fe
--- /dev/null
+++ b/libmultipath/prioritizers/upcall.c
@@ -0,0 +1,25 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#include <prio.h>
+#include <structs.h>
+
+int getprio (struct path * pp, char * args)
+{
+ char* cmd;
+ int ret = asprintf(&cmd, "%s %s", args, pp->dev);
+ if (ret == -1)
+ return -1;
+ FILE* pipe = popen( cmd, "r" );
+ free(cmd);
+ int prio;
+ int count = fscanf(pipe, "%i", &prio);
+ ret = pclose(pipe);
+ if (ret != 0)
+ return -1;
+ if (count != 1)
+ return -1;
+ return prio;
+}
diff --git a/multipath/multipath.conf.5 b/multipath/multipath.conf.5
index 0d4df0f..d8d6ad6 100644
--- a/multipath/multipath.conf.5
+++ b/multipath/multipath.conf.5
@@ -217,6 +217,9 @@ Generate a random priority between 1 and 10.
Generate the path priority based on the regular expression and the
priority provided as argument. requires prio_args keyword.
.TP
+.B upcall
+Call an external program to calculate the priority.
+.TP
Default value is \fBnone\fR.
.RE
.TP
@@ -243,6 +246,9 @@ If
.I exclusive_pref_bit
is set, paths with the TPGS pref bit set will always be in their own path
group.
+.TP
+.B upcall
+Cmdline to execute to determine device priority. The name of the component device of interest is added as the last argument.
.RE
.TP
.B features
--
2.8.0
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