Re: [Qemu-devel] [PATCH] docs: add blkdebug block driver documentation

[Eric Blake <eblake@redhat.com>]

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On 09/22/2014 03:20 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 <stefanha@redhat.com>
> ---
>  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 @@

No worse than many other files in this directory for omitting copyright
and license information (which means it inherits the default of GPLv2+
from the top-level).

> +
> +Rules can be placed in a .ini file:

Choice of article depends on whether you pronounce it "a dot-innie" or
"an eye-en-eye" file.

> +
> +  $ cat blkdebug.conf

This file suffix is not '.ini'.  So the idea is more that it is a
configuration file that uses '.ini' style parsing, and not that it is an
actual '.ini' file.

> +  [inject-error]
> +  event = "read_aio"
> +  errno = "28"
> +
> +This rule fails all aio read requests with ENOSPC (28).

Eeesh - we are really tying things to host-dependent errno values?
Might be worth a paragraph explaining that ENOSPC is not always 28.  Or
a design improvement to the setup to allow symbolic naming of the
desired actions. Or both.

> +
> +  errno - the POSIX errno value to return when a request matches this rule
> +

Again, POSIX doesn't proscribe errno values, just symbolic names; and
those names differ in values across different OS.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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