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

Eric Sandeen
2012-11-16T04:16:16Z

On 11/15/12 7:14 PM, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> 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@redhat.com>
> ---
> 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