[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Bug 1877384] Re: 9pfs file create with mapped-xattr can fail on overlay
From: |
Christian Schoenebeck |
Subject: |
[Bug 1877384] Re: 9pfs file create with mapped-xattr can fail on overlayfs |
Date: |
Thu, 10 Dec 2020 13:49:23 -0000 |
Good to know. Then it makes sense to close this report for now. Feel
free to reopen it if necessary.
Thanks!
** Changed in: qemu
Status: Confirmed => Incomplete
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1877384
Title:
9pfs file create with mapped-xattr can fail on overlayfs
Status in QEMU:
Incomplete
Bug description:
QEMU Version: 3.1.0 as packaged in debian buster, but the code appears to do
the same in master.
qemu command-line: qemu-system-x86_64 -m 1G -nographic -nic
"user,model=virtio-net-pci,tftp=$(pwd),net=10.0.2.0/24,host=10.0.2.2" -fsdev
local,id=fs,path=$thisdir/..,security_model=mapped-xattr -device
virtio-9p-pci,fsdev=fs,mount_tag=fs -drive
"file=$rootdisk,if=virtio,format=raw" -kernel "$kernel" -initrd "$initrd"
-append "$append"
I'm using CI that runs in a Docker container and runs a qemu VM with code and
results shared via virtio 9p.
The 9p fsdev is configured with security_model=mapped-xattr
When the test code attempts to create a log file in an existing directory,
open with O_CREAT fails with -ENOENT.
The relevant strace excerpt is:
28791 openat(11, ".", O_RDONLY|O_NOFOLLOW|O_PATH|O_DIRECTORY) = 20
28791 openat(20, "src", O_RDONLY|O_NOCTTY|O_NONBLOCK|O_NOFOLLOW|O_DIRECTORY)
= 21
28791 fcntl(21, F_SETFL, O_RDONLY|O_DIRECTORY) = 0
28791 close(20) = 0
28791 openat(21, "client.log",
O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK|O_NOFOLLOW, 0600) = 20
28791 fcntl(20, F_SETFL, O_WRONLY|O_CREAT|O_NONBLOCK|O_NOFOLLOW) = 0
28791 lsetxattr("/proc/self/fd/21/client.log", "user.virtfs.uid", "\0\0\0",
4, 0) = -1 ENOENT (No such file or directory)
My hypothesis for what's going wrong is since the Docker container's
overlayfs copies-up on writes, when it opens the file it's created a
new version of the `src` directory containing a `client.log`, but this
new src directory isn't accessible by file descriptor 20 and the
lsetxattr call is instead attempting to set attributes on the path in
the old `src` directory.
Looking at the code, a fix would be to change `hw/9pfs/9p-local.c` and
change `local_open2` to instead of calling `local_set_xattrat` to set
the xattrs by directory file descriptor and file name, to have a
version of local_set_xattrat` which uses `fsetxattr` to set the virtfs
attributes instead of the `fsetxattrat_nofollow` helper.
This reliably happened for me in CI, but I don't have access to the CI
host or the time to strip the test down to make a minimal test case,
and had difficulty reproducing the error on other machines.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1877384/+subscriptions