[v2,0/6] 9pfs: Fix ftruncate-after-unlink

Message

Greg Kurz March 11, 2025, 5:28 p.m. UTC

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

This v2 has a qtest as suggested by Christian Schoenebeck.

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          |  9 +++++
 10 files changed, 213 insertions(+), 18 deletions(-)