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Re: [libvirt] [PATCH v2 5/6] util: Add helpers for safe domain console operations



On 12/07/2011 11:08 AM, Peter Krempa wrote:
> This patch adds a set of functions used in creating console streams for
> domains using PTYs and ensures mutualy exculsive access to the PTYs.

s/mutualy exculsive/mutually exclusive/

> 
> If mutualy exclusive access is not used, two clients may open the same

s/mutualy/mutually/

> console, which results into corruption on both clients as both of them

s/into/in/

> race to read data from the PTY.
> 
> Two approaches are used to ensure this:
> 1) Internal data structure holding open PTYs.
>         This is used internaly and enables the user to forcibly

s/internaly/internally/

>         terminate another console connection eg. when somebody leaves
>         the console open on another host.
> 
> 2) UUCP style lock files:
>         This uses UUCP lock files according to the  FHS
>         ( http://www.pathname.com/fhs/pub/fhs-2.3.html#VARLOCKLOCKFILES )

Looks like I've got some reading to do.

>         to check if other programs (like minicom) are not using the pty
>         device of the console.
> 
>         This feature is disabled by default and may be enabled using
>         configure parameter
>         --with-console-lock-files=/path/to/lock/file/directory
>         or --with-console-lock-files=auto (which tries to infer the
>         location from OS used (currently only linux).
> 
>         On usual linux systems, normal users may not write to the
>         /var/lock directory containing the locks. This poses problems
>         while in session mode. If the current user has no access to the
>         lockfile directory, check for presence of the file is still
>         done, but no lock file is created. This does NOT result into an
>         error.
> 
> *  configure.ac
>         - add option to enable UUCP style PTY file locks
> *  src/Makefile.am
>         - add new files to be built with util module
> *  src/libvirt_private.syms
>         - add private symbol definition
> *  src/util/domain_safe_console.c
>         - implementation of safe console handling
> *  src/util/domain_safe_console.h
>         - header files
> ---
>  configure.ac                   |   37 +++-
>  src/Makefile.am                |    5 +-
>  src/libvirt_private.syms       |    6 +
>  src/util/domain_safe_console.c |  399 ++++++++++++++++++++++++++++++++++++++++
>  src/util/domain_safe_console.h |   28 +++
>  5 files changed, 466 insertions(+), 9 deletions(-)
>  create mode 100644 src/util/domain_safe_console.c
>  create mode 100644 src/util/domain_safe_console.h

I've run out of time to finish my review of this today, but the idea
seems interesting.

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

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