Alexander Graf <address@hidden> wrote on 2014/07/14 17:46:18:
On 14.07.14 17:38, Joakim Tjernlund wrote:
Alexander Graf <address@hidden> wrote on 2014/07/14 17:21:33:
From: Alexander Graf <address@hidden>
To: Joakim Tjernlund <address@hidden>,
Cc: address@hidden
Date: 2014/07/14 17:21
Subject: Re: [PATCH] linux-user: Add binfmt wrapper
On 14.07.14 16:38, Joakim Tjernlund wrote:
The popular binfmt-wrapper patch adds an additional
executable which mangle argv suitable for binfmt flag P.
In a chroot you need the both (statically linked) qemu-$arch
and qemu-$arch-binfmt-wrapper. This is sub optimal and a
better approach is to recognize the -binfmt-wrapper extension
within linux-user(qemu-$arch) and mangle argv there.
This just produces on executable which can be either copied to
the chroot or bind mounted with the appropriate -binfmt-wrapper
suffix.
Signed-off-by: Joakim Tjernlund <address@hidden>
Please make sure to CC Riku on patches like this - he is the
linux-user
maintainer.
Doesn't he read the devel list? Anyhow CC:ed
He may or may not. Qemu-devel can be pretty high volume :).
---
linux-user/main.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/linux-user/main.c b/linux-user/main.c
index 71a33c7..212067a 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -3828,6 +3828,19 @@ int main(int argc, char **argv, char **envp)
int i;
int ret;
int execfd;
+ char *binfmt;
+
+ i = strlen( argv[0] ) - strlen ( "-binfmt-wrapper" );
The spaces are odd. Did this patch pass checkpatch.pl? Same comment
goes
for almost all function invocations.
ehh, didn't run it through checkpatch.pl. Easy to fix next time.
+ binfmt = argv[0] + i;
+ if (i > 0 && strcmp ( binfmt, "-binfmt-wrapper" ) == 0) {
This magic needs to be documented somewhere. In fact, I find it
pretty
hard to use in real world scenarios. Imagine a distribution - should
it
package every target binary twice? Should it create hardlinks all
over?
How does dists. handle your original binfmt-wrapper? This is not much
different I think. Here you got a choice to create a hardlink or a
copy.
Any chroot will only have to bind mount binfmt-wrapper into the chroot
or
lxc container.
Yeah, and there are reasons my original approach isn't upstream :).
What are those then? Hardly just packaging problem/choise.
I think we should try and find better magic :). Looking at the
binfmt_misc loading code, I think we can cheat a bit. If we pass the
'O'
flag (open target binary for handler), binfmt_misc will tell us the
binary fd in AT_EXECFD:
NEW_AUX_ENT(AT_EXECFD, bprm->interp_data);
We could then use this as a hint that we were spawned by binfmt_misc
rather than directly and interpret the first argv as target_argv[0].
Then we can also add the P and O flags to scripts/qemu-binfmt-conf.sh
and have a solution that works well for everyone.
What to do with P only then? Seems like most dists uses only P
If a distro uses the P flag it's not using upstream code, so they have
to deal with their own breakage :). Fortunately the binfmt install
scripts are usually part of a package too, so they can be updated
easily.
scripts/qemu-binfmt-conf.sh does not use any flag currently, I don't think
that works either with current linux-user and choot/lxc
You think everyone feel OK with new defaults like OP ?