Revision 35991652baa12ff3d0e420c0d0cb2ad9f7076e5b authored by Mikulas Patocka on 02 June 2012, 23:29:58 UTC, committed by Alasdair G Kergon on 02 June 2012, 23:29:58 UTC
After the failure of a group of paths, any alternative paths that need initialising do not become available until further I/O is sent to the device. Until this has happened, ioctls return -EAGAIN. With this patch, new paths are made available in response to an ioctl too. The processing of the ioctl gets delayed until this has happened. Instead of returning an error, we submit a work item to kmultipathd (that will potentially activate the new path) and retry in ten milliseconds. Note that the patch doesn't retry an ioctl if the ioctl itself fails due to a path failure. Such retries should be handled intelligently by the code that generated the ioctl in the first place, noting that some SCSI commands should not be retried because they are not idempotent (XOR write commands). For commands that could be retried, there is a danger that if the device rejected the SCSI command, the path could be errorneously marked as failed, and the request would be retried on another path which might fail too. It can be determined if the failure happens on the device or on the SCSI controller, but there is no guarantee that all SCSI drivers set these flags correctly. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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Kconfig
config SYSFS
bool "sysfs file system support" if EXPERT
default y
help
The sysfs filesystem is a virtual filesystem that the kernel uses to
export internal kernel objects, their attributes, and their
relationships to one another.
Users can use sysfs to ascertain useful information about the running
kernel, such as the devices the kernel has discovered on each bus and
which driver each is bound to. sysfs can also be used to tune devices
and other kernel subsystems.
Some system agents rely on the information in sysfs to operate.
/sbin/hotplug uses device and object attributes in sysfs to assist in
delegating policy decisions, like persistently naming devices.
sysfs is currently used by the block subsystem to mount the root
partition. If sysfs is disabled you must specify the boot device on
the kernel boot command line via its major and minor numbers. For
example, "root=03:01" for /dev/hda1.
Designers of embedded systems may wish to say N here to conserve space.
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