Re: [Qemu-devel] [PATCH v3] docs: add blkdebug block driver documentation
Am 24.09.2014 um 11:44 hat Stefan Hajnoczi geschrieben: The blkdebug block driver is undocumented. Documenting it is worthwhile since it offers powerful error injection features that are used by qemu-iotests test cases. This document will make it easier for people to learn about and use blkdebug. Signed-off-by: Stefan Hajnoczi stefa...@redhat.com Thanks, applied to the block branch. Kevin
[Qemu-devel] [PATCH v3] docs: add blkdebug block driver documentation
The blkdebug block driver is undocumented. Documenting it is worthwhile since it offers powerful error injection features that are used by qemu-iotests test cases. This document will make it easier for people to learn about and use blkdebug. Signed-off-by: Stefan Hajnoczi stefa...@redhat.com --- v3: * Fix tab space damage [Eric] * Rephrase event_names[] as full list of events [Eric] * Explain that blkdebug state is not observable from outside [Eric] * Clarify state 0 and state 1 [Eric] v2: * Added GPL v2 or later license and Red Hat copyright [Eric] * Expanded ini rules file explanation [Paolo] * Added note that errno values depend on the host [Eric] docs/blkdebug.txt | 161 ++ 1 file changed, 161 insertions(+) create mode 100644 docs/blkdebug.txt diff --git a/docs/blkdebug.txt b/docs/blkdebug.txt new file mode 100644 index 000..5dde072 --- /dev/null +++ b/docs/blkdebug.txt @@ -0,0 +1,161 @@ +Block I/O error injection using blkdebug + +Copyright (C) 2014 Red Hat Inc + +This work is licensed under the terms of the GNU GPL, version 2 or later. See +the COPYING file in the top-level directory. + +The blkdebug block driver is a rule-based error injection engine. It can be +used to exercise error code paths in block drivers including ENOSPC (out of +space) and EIO. + +This document gives an overview of the features available in blkdebug. + +Background +-- +Block drivers have many error code paths that handle I/O errors. Image formats +are especially complex since metadata I/O errors during cluster allocation or +while updating tables happen halfway through request processing and require +discipline to keep image files consistent. + +Error injection allows test cases to trigger I/O errors at specific points. +This way, all error paths can be tested to make sure they are correct. + +Rules +- +The blkdebug block driver takes a list of rules that tell the error injection +engine when to fail an I/O request. + +Each I/O request is evaluated against the rules. If a rule matches the request +then its action is executed. + +Rules can be placed in a configuration file; the configuration file +follows the same .ini-like format used by QEMU's -readconfig option, and +each section of the file represents a rule. + +The following configuration file defines a single rule: + + $ cat blkdebug.conf + [inject-error] + event = read_aio + errno = 28 + +This rule fails all aio read requests with ENOSPC (28). Note that the errno +value depends on the host. On Linux, see +/usr/include/asm-generic/errno-base.h for errno values. + +Invoke QEMU as follows: + + $ qemu-system-x86_64 +-drive if=none,cache=none,file=blkdebug:blkdebug.conf:test.img,id=drive0 \ +-device virtio-blk-pci,drive=drive0,id=virtio-blk-pci0 + +Rules support the following attributes: + + event - which type of operation to match (e.g. read_aio, write_aio, + flush_to_os, flush_to_disk). See the Events section for + information on events. + + state - (optional) the engine must be in this state number in order for this + rule to match. See the State transitions section for information + on states. + + errno - the numeric errno value to return when a request matches this rule. + The errno values depend on the host since the numeric values are not + standarized in the POSIX specification. + + sector - (optional) a sector number that the request must overlap in order to + match this rule + + once - (optional, default off) only execute this action on the first + matching request + + immediately - (optional, default off) return a NULL BlockDriverAIOCB +pointer and fail without an errno instead. This exercises the +code path where BlockDriverAIOCB fails and the caller's +BlockDriverCompletionFunc is not invoked. + +Events +-- +Block drivers provide information about the type of I/O request they are about +to make so rules can match specific types of requests. For example, the qcow2 +block driver tells blkdebug when it accesses the L1 table so rules can match +only L1 table accesses and not other metadata or guest data requests. + +The core events are: + + read_aio - guest data read + + write_aio - guest data write + + flush_to_os - write out unwritten block driver state (e.g. cached metadata) + + flush_to_disk - flush the host block device's disk cache + +See block/blkdebug.c:event_names[] for the full list of events. You may need +to grep block driver source code to understand the meaning of specific events. + +State transitions +- +There are cases where more power is needed to match a particular I/O request in +a longer sequence of requests. For example: + + write_aio + flush_to_disk + write_aio + +How do we match the 2nd write_aio but not the first? This is where state
Re: [Qemu-devel] [PATCH v3] docs: add blkdebug block driver documentation
The Wednesday 24 Sep 2014 à 10:44:14 (+0100), Stefan Hajnoczi wrote : The blkdebug block driver is undocumented. Documenting it is worthwhile since it offers powerful error injection features that are used by qemu-iotests test cases. This document will make it easier for people to learn about and use blkdebug. Signed-off-by: Stefan Hajnoczi stefa...@redhat.com --- v3: * Fix tab space damage [Eric] * Rephrase event_names[] as full list of events [Eric] * Explain that blkdebug state is not observable from outside [Eric] * Clarify state 0 and state 1 [Eric] v2: * Added GPL v2 or later license and Red Hat copyright [Eric] * Expanded ini rules file explanation [Paolo] * Added note that errno values depend on the host [Eric] docs/blkdebug.txt | 161 ++ 1 file changed, 161 insertions(+) create mode 100644 docs/blkdebug.txt diff --git a/docs/blkdebug.txt b/docs/blkdebug.txt new file mode 100644 index 000..5dde072 --- /dev/null +++ b/docs/blkdebug.txt @@ -0,0 +1,161 @@ +Block I/O error injection using blkdebug + +Copyright (C) 2014 Red Hat Inc + +This work is licensed under the terms of the GNU GPL, version 2 or later. See +the COPYING file in the top-level directory. + +The blkdebug block driver is a rule-based error injection engine. It can be +used to exercise error code paths in block drivers including ENOSPC (out of +space) and EIO. + +This document gives an overview of the features available in blkdebug. + +Background +-- +Block drivers have many error code paths that handle I/O errors. Image formats +are especially complex since metadata I/O errors during cluster allocation or +while updating tables happen halfway through request processing and require +discipline to keep image files consistent. + +Error injection allows test cases to trigger I/O errors at specific points. +This way, all error paths can be tested to make sure they are correct. + +Rules +- +The blkdebug block driver takes a list of rules that tell the error injection +engine when to fail an I/O request. + +Each I/O request is evaluated against the rules. If a rule matches the request +then its action is executed. + +Rules can be placed in a configuration file; the configuration file +follows the same .ini-like format used by QEMU's -readconfig option, and +each section of the file represents a rule. + +The following configuration file defines a single rule: + + $ cat blkdebug.conf + [inject-error] + event = read_aio + errno = 28 + +This rule fails all aio read requests with ENOSPC (28). Note that the errno +value depends on the host. On Linux, see +/usr/include/asm-generic/errno-base.h for errno values. + +Invoke QEMU as follows: + + $ qemu-system-x86_64 +-drive if=none,cache=none,file=blkdebug:blkdebug.conf:test.img,id=drive0 \ +-device virtio-blk-pci,drive=drive0,id=virtio-blk-pci0 + +Rules support the following attributes: + + event - which type of operation to match (e.g. read_aio, write_aio, + flush_to_os, flush_to_disk). See the Events section for + information on events. + + state - (optional) the engine must be in this state number in order for this + rule to match. See the State transitions section for information + on states. + + errno - the numeric errno value to return when a request matches this rule. + The errno values depend on the host since the numeric values are not + standarized in the POSIX specification. + + sector - (optional) a sector number that the request must overlap in order to + match this rule + + once - (optional, default off) only execute this action on the first + matching request + + immediately - (optional, default off) return a NULL BlockDriverAIOCB +pointer and fail without an errno instead. This exercises the +code path where BlockDriverAIOCB fails and the caller's +BlockDriverCompletionFunc is not invoked. + +Events +-- +Block drivers provide information about the type of I/O request they are about +to make so rules can match specific types of requests. For example, the qcow2 +block driver tells blkdebug when it accesses the L1 table so rules can match +only L1 table accesses and not other metadata or guest data requests. + +The core events are: + + read_aio - guest data read + + write_aio - guest data write + + flush_to_os - write out unwritten block driver state (e.g. cached metadata) + + flush_to_disk - flush the host block device's disk cache + +See block/blkdebug.c:event_names[] for the full list of events. You may need +to grep block driver source code to understand the meaning of specific events. + +State transitions +- +There are cases where
Re: [Qemu-devel] [PATCH v3] docs: add blkdebug block driver documentation
On 09/24/2014 12:24 PM, Max Reitz wrote: On 24.09.2014 11:44, Stefan Hajnoczi wrote: The blkdebug block driver is undocumented. Documenting it is worthwhile since it offers powerful error injection features that are used by qemu-iotests test cases. This document will make it easier for people to learn about and use blkdebug. Signed-off-by: Stefan Hajnoczi stefa...@redhat.com --- v3: * Fix tab space damage [Eric] * Rephrase event_names[] as full list of events [Eric] * Explain that blkdebug state is not observable from outside [Eric] * Clarify state 0 and state 1 [Eric] v2: * Added GPL v2 or later license and Red Hat copyright [Eric] * Expanded ini rules file explanation [Paolo] * Added note that errno values depend on the host [Eric] docs/blkdebug.txt | 161 ++ 1 file changed, 161 insertions(+) create mode 100644 docs/blkdebug.txt Reviewed-by: Max Reitz mre...@redhat.com Maybe I'll add information about blkdebug's QMP interface sometime... If you have the cycles and the knowledge, you definitely should!
Re: [Qemu-devel] [PATCH v3] docs: add blkdebug block driver documentation
On 24.09.2014 11:44, Stefan Hajnoczi wrote: The blkdebug block driver is undocumented. Documenting it is worthwhile since it offers powerful error injection features that are used by qemu-iotests test cases. This document will make it easier for people to learn about and use blkdebug. Signed-off-by: Stefan Hajnoczi stefa...@redhat.com --- v3: * Fix tab space damage [Eric] * Rephrase event_names[] as full list of events [Eric] * Explain that blkdebug state is not observable from outside [Eric] * Clarify state 0 and state 1 [Eric] v2: * Added GPL v2 or later license and Red Hat copyright [Eric] * Expanded ini rules file explanation [Paolo] * Added note that errno values depend on the host [Eric] docs/blkdebug.txt | 161 ++ 1 file changed, 161 insertions(+) create mode 100644 docs/blkdebug.txt Reviewed-by: Max Reitz mre...@redhat.com Maybe I'll add information about blkdebug's QMP interface sometime...
Re: [Qemu-devel] [PATCH v3] docs: add blkdebug block driver documentation
On 09/24/2014 03:44 AM, Stefan Hajnoczi wrote: The blkdebug block driver is undocumented. Documenting it is worthwhile since it offers powerful error injection features that are used by qemu-iotests test cases. This document will make it easier for people to learn about and use blkdebug. Signed-off-by: Stefan Hajnoczi stefa...@redhat.com --- v3: * Fix tab space damage [Eric] * Rephrase event_names[] as full list of events [Eric] * Explain that blkdebug state is not observable from outside [Eric] * Clarify state 0 and state 1 [Eric] Thanks for the updates. Reviewed-by: Eric Blake ebl...@redhat.com + +The error injection engine has an integer called the state that always starts +initialized to 1. The state integer is internal to blkdebug and cannot be +observed from outside but rules can interact with it for powerful matching +behavior. + We could always expose it and update the documentation in a later patch. But it is fair to document the current state of things (current docs are always better than no docs :) -- Eric Blake eblake redhat com+1-919-301-3266 Libvirt virtualization library http://libvirt.org signature.asc Description: OpenPGP digital signature
