On Monday, March 10, 2025 6:10:57 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
>
> Christian,
>
> I'm not familiar enough with the latest changes to write a proper test
> for this case and I don't have enough cycles to learn. I'm sorry for that
> but I guess it will be a lot easier for you and I'll review.
With the following test client patch applied:
https://lore.kernel.org/all/e1trx7r-002jej...@kylie.crudebyte.com/
then something like this should do it:
diff --git a/tests/qtest/virtio-9p-test.c b/tests/qtest/virtio-9p-test.c
index f515a9bb15..d15721e4b2 100644
--- a/tests/qtest/virtio-9p-test.c
+++ b/tests/qtest/virtio-9p-test.c
@@ -736,6 +736,12 @@ static void fs_use_after_unlink(void *obj, void *data,
.data = buf
}).count;
g_assert_cmpint(count, ==, write_count);
+ tsetattr({ /* truncate file to (arbitrarily chosen) size 2001 */
+ .client = v9p, .fid = fid_file, .attr = (v9fs_attr) {
+ .valid = P9_SETATTR_SIZE,
+ .size = 2001
+ }
+ });
}
static void cleanup_9p_local_driver(void *data)
/Christian
> Cheers,
>
> --
> Greg
>
> Greg Kurz (4):
> 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
>
> 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 ++++
> 7 files changed, 122 insertions(+), 17 deletions(-)
>
>
