[PATCH 0/6] xfs_io: fix up command iteration

[Dave Chinner <david@fromorbit.com>]

Hi folks,

Here are teh changes I've put together to address the command
iteration problems that xfs_io is demonstrating. I described the
history that lead us to the current problems here:

https://www.spinics.net/lists/fstests/msg04572.html

This series cleans up the libxcmd command code and fixes the xfs_io
problems without completely removing the existing iteration
behaviour.

The first three patches address the "args_command" abstraction,
renaming it to a "command iterator" abstraction and clean up the
command loop implementation to make it easier to follow. It is now
clear that the the command loop has an external command iterator
control function, and it has a clean and clear mechanism for the
external commands to prevent iteration from occurring
(CMD_FLAG_ONESHOT).

The fourth patch cleans up a recent change made to the xfs_quota
interface to support foreign filesystems - it still needs to be abel
to run the help and quit commands regardless of other state. The
same requirement exists for xfs_io, it just implemented the command
check that allowed them to be run differently. This patch
centralises that by marking libxcmd functions as "library" functions
and skips the application provided command checking altogether.
Hence the apps no longer need to handle these cases at all.

The fifth patch makes all the xfs_io commands that shouldn't iterate
the file table one-shot only commands. This avoids all the nasty
problems with commands like open that end up completely filling
the open file table with thousands of filedescriptors pointing to
the same file. THis makes those commands usable and predictable.

Finally, the last patch adds CLI support for running xfs_io commands
as one-shot commands rather than iterating commands. This is useful
for being able to set up multiple files and operate on them as a
whole or individually as necessary. This patch also documents in the
man page that some commands may iterate all open files and that the
new "-C" command option can be used to avoid problems arising from
this historical behaviour.

-Dave.