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Re: [Qemu-devel] [PATCH] docs: add blkdebug block driver documentation
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] docs: add blkdebug block driver documentation |
Date: |
Mon, 22 Sep 2014 12:16:18 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 |
Il 22/09/2014 11:20, Stefan Hajnoczi ha scritto:
> 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.
Just one small comment below...
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> docs/blkdebug.txt | 142
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 142 insertions(+)
> create mode 100644 docs/blkdebug.txt
>
> diff --git a/docs/blkdebug.txt b/docs/blkdebug.txt
> new file mode 100644
> index 0000000..7e616e0
> --- /dev/null
> +++ b/docs/blkdebug.txt
> @@ -0,0 +1,142 @@
> +Block I/O error injection using blkdebug
> +----------------------------------------
> +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 .ini file:
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"
> +
Paolo