Re: [PATCH v3 0/6] 9pfs: Fix ftruncate-after-unlink

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Wednesday, March 12, 2025 4:29:26 PM CET Greg Kurz wrote:
> QEMU 9.2 already fixed the long standing limitation of failing fstat() on
> unlinked files. This series does something similar for ftruncate().
> 
> The following program can be straced inside the guest with a shared fs in
> passthrough mode over 9p2000.L.
> 
> int main(void)
> {
> 	struct stat st;
> 	int fd = creat("./foo", 0000);
> 
> 	ftruncate(fd, 100);
> 	unlink("./foo");
> 	ftruncate(fd, 1000);
> }
> 
> Before :
> 
> creat("./foo", 000)                     = 3
> ftruncate(3, 100)                       = -1 EACCES (Permission denied)
> unlink("./foo")                         = 0
> ftruncate(3, 1000)                      = -1 ENOENT (No such file or directory)
> 
> After :
> 
> creat("./foo", 000)                     = 3
> ftruncate(3, 100)                       = 0
> unlink("./foo")                         = 0
> ftruncate(3, 1000)                      = 0
> 
> Cheers,
> 
> --
> Greg
> 
> Christian Schoenebeck (1):
>   tests/9p: add 'Tsetattr' request to test client
> 
> Greg Kurz (5):
>   9pfs: local : Introduce local_fid_fd() helper
>   9pfs: Don't use file descriptors in core code
>   9pfs: Introduce ftruncate file op
>   9pfs: Introduce futimens file op
>   tests/9p: Test `Tsetattr` can truncate unlinked file
> 
>  fsdev/file-op-9p.h                    |  5 +++
>  hw/9pfs/9p-local.c                    | 49 ++++++++++++++++++++-------
>  hw/9pfs/9p-synth.c                    | 22 ++++++++++++
>  hw/9pfs/9p-util.h                     |  1 +
>  hw/9pfs/9p.c                          | 21 +++++++++---
>  hw/9pfs/cofs.c                        | 37 ++++++++++++++++++++
>  hw/9pfs/coth.h                        |  4 +++
>  tests/qtest/libqos/virtio-9p-client.c | 49 +++++++++++++++++++++++++++
>  tests/qtest/libqos/virtio-9p-client.h | 34 +++++++++++++++++++
>  tests/qtest/virtio-9p-test.c          | 15 ++++++++
>  10 files changed, 219 insertions(+), 18 deletions(-)
> 
>

Queued on 9p.next:
https://github.com/cschoenebeck/qemu/commits/9p.next

Thanks!

/Christian