Add warning for zfs_vdev_elevator option removal

Originally the zfs_vdev_elevator module option was added as a
convenience so the requested elevator would be automatically set
on the underlying block devices.  At the time this was simple
because the kernel provided an API function which did exactly this.

This API was then removed in the Linux 4.12 kernel which prompted
us to add compatibly code to set the elevator via a usermodehelper.
While well intentioned this introduced a bug which could cause a
system hang, that issue was subsequently fixed by commit 2a0d4188.

In order to avoid future bugs in this area, and to simplify the code,
this functionality is being deprecated.  A console warning has been
added to notify any existing consumers and the documentation updated
accordingly.  This option will remain for the lifetime of the 0.8.x
series for compatibility but if planned to be phased out of master.

Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #8664
Closes #9317

diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index d9be70e235a4663f3437b14f189bc512852f346b..c711f6de61bfd07e4c2ec4f57bac136ac3072815 100644 (file)
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -3188,8 +3188,10 @@ Default value: \fB32,768\fR.
 \fBzfs_vdev_scheduler\fR (charp)
 .ad
 .RS 12n
-Set the Linux I/O scheduler on whole disk vdevs to this scheduler. Valid options
-are noop, cfq, bfq & deadline
+Set the Linux I/O scheduler on whole disk vdevs to this scheduler.  This
+option has been deprecated and will be removed in a future release.  The
+standard \fB/sys/block/<block>/queue/scheduler\fR interface should be used
+to set a block device scheduler.
 .sp
 Default value: \fBnoop\fR.
 .RE

diff --git a/module/os/linux/zfs/vdev_disk.c b/module/os/linux/zfs/vdev_disk.c
index d223ef3b30ae0e0c5f00aba9970b16211fbeed2f..8490f1db16f152b5cd7461a82b6da6f47d3fa471 100644 (file)
--- a/module/os/linux/zfs/vdev_disk.c
+++ b/module/os/linux/zfs/vdev_disk.c
@@ -930,7 +930,14 @@ param_set_vdev_scheduler(const char *val, zfs_kernel_param_t *kp)
                mutex_exit(&spa_namespace_lock);
        }
 
-       return (param_set_charp(val, kp));
+
+       int error = param_set_charp(val, kp);
+       if (error == 0) {
+               printk(KERN_INFO "The 'zfs_vdev_scheduler' module option "
+                   "will be removed in a future release.\n");
+       }
+
+       return (error);
 }
 
 vdev_ops_t vdev_disk_ops = {