[Toybox] [NEW TOYS] hardware rescan tool, FIFREEZE/FITHAW wrapper...(possibly out of scope?)

[Rob Landley]

On 03/29/14 02:22, Isaac Dunham wrote:
> I've written a couple of new toys that might well be out of
> scope, but might be interesting or useful "for parts".
>
> I'll describe the commands and the use cases.

Ok.

> 1-hwrs:
> This was originally intended as a SUID helper cludge for my
> Acer Aspire One, which has a PCI-bus based SD card reader
> that only shows up when the SD card is inserted. Kernel PCI
> hotplug does not work properly, with the card reader frequently
> failing to show up, dmesg getting spammed when I enable it,
> and the wireless card sporadically failing for reasons that
> seem to be related. However, it works to manually trigger a
> PCI bus rescan. Additionally, neither mdev nor udev (as
> configured in Debian Squeeze)  probe for partitions on slow
> external media, which makes configuring a  user mount in
> /etc/fstab pointless.

They just respond to hotplug events.

The toybox mdev is only halfway implemented, and part of the
reason is devtmpfs exists now, so half of what mdev used to
do is unnecessary. It needs a bit of a redesign, and I haven't
gotten around to looking hard it since.

> I didn't want to have to log in as root every time I plugged
> in an SD card, so I wrote this. It simply triggers a PCI bus
> rescan (hwrs -p), then walks /dev opening every block device
> so as to make the kernel look for partitions (hwrs -b).

This does strike me as an mdev function... except that mdev isn't
currently an suid command. Normal users can't trigger any useful
behavior out of mdev, and trying to add that capability opens fun holes
where mdev is called as /sbin/hotplug and does something based on
environment variables...

I can distinguish suid from actual root via getuid() != geteuid() and
just have TOYBOX_STAYROOT without TOYBOX_NEEDROOT and then do the "if
(!geteuid() && getuid() && setuid(getuid())) perror_exit("setuid");"
dance that main.c is currently doing. (I'm aware this ignores capability
bits, and am actually pretty happy about that.)

> Default behavior is the same as hwrs -pb.
> The sole reason I wrote it as a new toy was that was the
> quickest way to get it done.
>
> If you think that this isn't in scope but the probe for
> partitions sounds interesting for mdev, I'd be happy to write
> that.

I think a command line option to tell mdev to give the PCI bus a good
smack and then rescan all the block devices sounds fine. It's not the
default behavior, but an mdev command line option (possibly with a
config option) is probably where this belongs.

> (Coincidentally, I've thought of a way to make mdev
> handle hotplugging with minimal code changes: use the environment
> to find the right uevent file.)

The one I wrote for busybox did hotplugging. The busybox one has changed
a huge amount since then and I want to read up on it to see if people
have expectations. I also want to make it work well with devtmpfs.

I also need to figure out what horrible things <strike>devfsd</strike>
<strike>hald</strike> systemd is doing in this area, so I can obsolete them.

> 2. xfs_freeze:
> This is only a wrapper for the FIFREEZE/FITHAW ioctls.

man 8 fsfreeze

Apparently part of util-linux since 2010 or so.

> The name is a historical artefact; this is a clone of the
> xfs_freeze utility from xfsprogs.

I renamed it to the generic one. (Then hit some strange command line
option parsing bug I need to fix when testing it, so haven't checked it
in yet...)

Thanks,

Rob