From d5f42aac0492617b4ceaae88d1583a71f411d6f9 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Mon, 14 Oct 2024 17:05:53 +0100 Subject: docs/devel/blkdebug: Convert to rST format Convert blkdebug.txt to rST format. We put it into index-build.rst because it falls under the "test" part of "QEMU Build and Test System". Signed-off-by: Peter Maydell Reviewed-by: Thomas Huth Message-id: 20240816132212.3602106-2-peter.maydell@linaro.org --- docs/devel/blkdebug.txt | 162 ------------------------------------ docs/devel/testing/blkdebug.rst | 177 ++++++++++++++++++++++++++++++++++++++++ docs/devel/testing/index.rst | 1 + 3 files changed, 178 insertions(+), 162 deletions(-) delete mode 100644 docs/devel/blkdebug.txt create mode 100644 docs/devel/testing/blkdebug.rst (limited to 'docs') diff --git a/docs/devel/blkdebug.txt b/docs/devel/blkdebug.txt deleted file mode 100644 index 0b0c128..0000000 --- a/docs/devel/blkdebug.txt +++ /dev/null @@ -1,162 +0,0 @@ -Block I/O error injection using blkdebug ----------------------------------------- -Copyright (C) 2014-2015 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 - standardized 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 BlockAIOCB - pointer and fail without an errno instead. This - exercises the code path where BlockAIOCB fails and the - caller's BlockCompletionFunc 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 qapi/block-core.json:BlkdebugEvent 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 -transitions come in. - -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. - -Rules can be conditional on the current state and they can transition to a new -state. - -When a rule's "state" attribute is non-zero then the current state must equal -the attribute in order for the rule to match. - -For example, to match the 2nd write_aio: - - [set-state] - event = "write_aio" - state = "1" - new_state = "2" - - [inject-error] - event = "write_aio" - state = "2" - errno = "5" - -The first write_aio request matches the set-state rule and transitions from -state 1 to state 2. Once state 2 has been entered, the set-state rule no -longer matches since it requires state 1. But the inject-error rule now -matches the next write_aio request and injects EIO (5). - -State transition 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 - - new_state - transition to this state number - -Suspend and resume ------------------- -Exercising code paths in block drivers may require specific ordering amongst -concurrent requests. The "breakpoint" feature allows requests to be halted on -a blkdebug event and resumed later. This makes it possible to achieve -deterministic ordering when multiple requests are in flight. - -Breakpoints on blkdebug events are associated with a user-defined "tag" string. -This tag serves as an identifier by which the request can be resumed at a later -point. - -See the qemu-io(1) break, resume, remove_break, and wait_break commands for -details. diff --git a/docs/devel/testing/blkdebug.rst b/docs/devel/testing/blkdebug.rst new file mode 100644 index 0000000..63887c9 --- /dev/null +++ b/docs/devel/testing/blkdebug.rst @@ -0,0 +1,177 @@ +Block I/O error injection using ``blkdebug`` +============================================ + +.. + Copyright (C) 2014-2015 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 `Events`_ for + information on events. + +``state`` + (optional) the engine must be in this state number in order for this + rule to match. See `State transitions`_ 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 + standardized 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 ``BlockAIOCB`` + pointer and fail without an errno instead. This + exercises the code path where ``BlockAIOCB`` fails and the + caller's ``BlockCompletionFunc`` 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 ``qapi/block-core.json:BlkdebugEvent`` 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 +transitions come in. + +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. + +Rules can be conditional on the current state and they can transition to a new +state. + +When a rule's "state" attribute is non-zero then the current state must equal +the attribute in order for the rule to match. + +For example, to match the 2nd write_aio:: + + [set-state] + event = "write_aio" + state = "1" + new_state = "2" + + [inject-error] + event = "write_aio" + state = "2" + errno = "5" + +The first ``write_aio`` request matches the ``set-state`` rule and transitions from +state 1 to state 2. Once state 2 has been entered, the ``set-state`` rule no +longer matches since it requires state 1. But the ``inject-error`` rule now +matches the next ``write_aio`` request and injects ``EIO`` (5). + +State transition 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 `Events`_ for + information on events. + +``state`` + (optional) the engine must be in this state number in order for this + rule to match + +``new_state`` + transition to this state number + +Suspend and resume +------------------ +Exercising code paths in block drivers may require specific ordering amongst +concurrent requests. The "breakpoint" feature allows requests to be halted on +a ``blkdebug`` event and resumed later. This makes it possible to achieve +deterministic ordering when multiple requests are in flight. + +Breakpoints on ``blkdebug`` events are associated with a user-defined ``tag`` string. +This tag serves as an identifier by which the request can be resumed at a later +point. + +See the ``qemu-io(1)`` ``break``, ``resume``, ``remove_break``, and ``wait_break`` +commands for details. diff --git a/docs/devel/testing/index.rst b/docs/devel/testing/index.rst index 45eb4a7..9e772c7 100644 --- a/docs/devel/testing/index.rst +++ b/docs/devel/testing/index.rst @@ -14,3 +14,4 @@ testing infrastructure. acpi-bits ci fuzzing + blkdebug -- cgit v1.1