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Re: [PATCH] xfs_quota: correctly initialise the default path

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs_quota: correctly initialise the default path
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Thu, 15 Nov 2012 22:18:20 -0600
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1353028488-24436-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1353028488-24436-1-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:16.0) Gecko/20121026 Thunderbird/16.0.2
On 11/15/12 7:14 PM, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> When we initial xfs_quota, we place lots of information into the
> fs_table. This includes all the devices/mount points the user has
> specified as a global command line parameter to report on, as well
> as all the paths under project quota control.
> 
> There is a "current path" pointer (fs_path) maintained by the code
> that points somewhere into the fs_table. After the table is
> initialised, fs_path always points to the last entry in the table,
> and hence has to be re-initialised to point at the desired entry
> before it can be used properly.
> 
> In the case of xfs_quota, if the command passed on the command line
> is a non-global command, the command is called multiple times, each
> time after the libxcmd args_command() callback is run. That starts
> with an index of 0, and until the callback returns zero it will keep
> passing whatever the last returned value was into the callback.
> 
> xfs_quota supplies such a callback, and it's purpose is to iterate
> over the fs_table setting fs_path to the next mount point in the
> table. IOWs, non-global quota functions get called once for each
> mount point specified on the command line. However, it also means
> that for global functions, the fs_path pointer is not
> re-initialised and hence if there are project quotas configured the
> fs_path pointer does not point to a mount point andhence commands
> may malfunction..
> 
> The problem that demonstrated this is the report function. It does
> it's own fs_table iteration if the command requires it, and so only
> should be called once to avoid outputting the same information
> multiple times.  That's what the previous patch fixed by making the
> command global, but this now has the effect of making commands that
> need to operate on the device specified on the global command rely
> on the fs_path variable pointing at that device.
> 
> Further, commands executed by the interactive method are always
> treated as global commands, so the report command never worked as a
> global command in the presence of a configured project quota setup.
> 
> Fix the problem by initialising the fs_path pointer correctly.

tl;dr ;)  I'm all for detailed commit messages but you lost me there.
If I were searching for this fix I'd have no idea what behavior this
commit actually . . . fixes. :)

Can you say:

a) what the "previous patch" commit was, and
b) what commandline triggers this problem, and what the result is?

Sorry if I'm dense,
-Eric


> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
>  quota/init.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/quota/init.c b/quota/init.c
> index 3293b90..0b481f7 100644
> --- a/quota/init.c
> +++ b/quota/init.c
> @@ -140,6 +140,15 @@ init(
>  
>       init_commands();
>       add_args_command(init_args_command);
> +
> +     /*
> +      * Ensure that global commands don't end up with an invalid path pointer
> +      * by setting the default device at the first specified on the CLI
> +      */
> +     if (argc != optind)
> +             fs_path = fs_table_lookup(argv[optind], FS_MOUNT_POINT);
> +     else
> +             fs_path = &fs_table[0];
>  }
>  
>  int
> 

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