[Qemu-devel] linux-user: enabling binfmt P flag

[Riku Voipio <riku.voipio@iki.fi>]

Hi,

After weekend, I think the solution to using the P flag is to
go back to Joakim's original patch:

http://lists.gnu.org/archive/html/qemu-devel/2014-07/msg02269.html

With this, we get:

If you continue to use qemu-x-static in your binfmt_misc registration,
nothing changes - both old and new qemu work using the old binfmt
registration.

If you rename the binary qemu-x-binfmt, you need to update the
binfmt_misc register to have P flag and new binary  - you get correct
argv with new qemu. Any old qemu you still have around, will stop
working. But with "file not found" error rather than obscurely eating
one of the arguments and running regardless.

This leaves us with one case - people who are used to running
qemu-x-static ./binary to test single binaries. Distro's will need
leave a symlink from qemu-x-binfmt qemu-x-static. The "-binfmt" string
check doesn't trigger, and qemu works as before.

The key point: this way nobody's working setup will break, unless they
update binfmt registration. As long as the change is done by users
them self (I need correct argv0 -> I will update binfmt), there is very
little surprise for anyone. 

There will be some fallout once *distributions* change the binfmt - users
will notice their existing qemu chroots stop working with a "file not
found" error for any binary they try to run.

If we find even this breakage too much, I'm not sure this can be fixed.

Riku