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 <peter.maydell@linaro.org>
---
At least, index-build seemed the most plausible home to me...
---
 MAINTAINERS                |   1 +
 docs/devel/blkdebug.rst    | 177 +++++++++++++++++++++++++++++++++++++
 docs/devel/blkdebug.txt    | 162 ---------------------------------
 docs/devel/index-build.rst |   1 +
 4 files changed, 179 insertions(+), 162 deletions(-)
 create mode 100644 docs/devel/blkdebug.rst
 delete mode 100644 docs/devel/blkdebug.txt

diff --git a/MAINTAINERS b/MAINTAINERS
index 3584d6a6c6d..ca0a5c731f5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4015,6 +4015,7 @@ M: Hanna Reitz <hreitz@redhat.com>
 L: qemu-block@nongnu.org
 S: Supported
 F: block/blkdebug.c
+F: docs/devel/blkdebug.rst
 
 vpc
 M: Kevin Wolf <kwolf@redhat.com>
diff --git a/docs/devel/blkdebug.rst b/docs/devel/blkdebug.rst
new file mode 100644
index 00000000000..63887c9aa9c
--- /dev/null
+++ b/docs/devel/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/blkdebug.txt b/docs/devel/blkdebug.txt
deleted file mode 100644
index 0b0c128d356..00000000000
--- 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/index-build.rst b/docs/devel/index-build.rst
index 90b406ca0ed..3a912aefcfa 100644
--- a/docs/devel/index-build.rst
+++ b/docs/devel/index-build.rst
@@ -18,3 +18,4 @@ the basics if you are adding new files and targets to the build.
    qapi-code-gen
    fuzzing
    control-flow-integrity
+   blkdebug
-- 
2.34.1

On 16/08/2024 15.22, Peter Maydell wrote:
> 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 <peter.maydell@linaro.org>
> ---
> At least, index-build seemed the most plausible home to me...

I recently split the testing docs into a separate folder, maybe it could 
also go there instead?

Anyway:
Reviewed-by: Thomas Huth <thuth@redhat.com>