On Wed, 21 Oct 2020 20:20:08 +0200
Christian Schoenebeck <qemu_...@crudebyte.com> wrote:
> On Mittwoch, 21. Oktober 2020 14:51:09 CEST Christian Schoenebeck wrote:
> > This test case uses a Tlink request to create a hard link to a regular
> > file using the 9pfs 'local' fs driver.
> >
> > Signed-off-by: Christian Schoenebeck <qemu_...@crudebyte.com>
> > ---
> > tests/qtest/virtio-9p-test.c | 71 ++++++++++++++++++++++++++++++++++++
> > 1 file changed, 71 insertions(+)
> >
> > diff --git a/tests/qtest/virtio-9p-test.c b/tests/qtest/virtio-9p-test.c
> > index 33cba24b18..460fa49fe3 100644
> > --- a/tests/qtest/virtio-9p-test.c
> > +++ b/tests/qtest/virtio-9p-test.c
> > @@ -260,6 +260,7 @@ static const char *rmessage_name(uint8_t id)
> > id == P9_RMKDIR ? "RMKDIR" :
> > id == P9_RLCREATE ? "RLCREATE" :
> > id == P9_RSYMLINK ? "RSYMLINK" :
> > + id == P9_RLINK ? "RLINK" :
> > id == P9_RUNLINKAT ? "RUNLINKAT" :
> > id == P9_RFLUSH ? "RFLUSH" :
> > id == P9_RREADDIR ? "READDIR" :
> > @@ -767,6 +768,33 @@ static void v9fs_rsymlink(P9Req *req, v9fs_qid *qid)
> > v9fs_req_free(req);
> > }
> >
> > +/* size[4] Tlink tag[2] dfid[4] fid[4] name[s] */
> > +static P9Req *v9fs_tlink(QVirtio9P *v9p, uint32_t dfid, uint32_t fid,
> > + const char *name, uint16_t tag)
> > +{
> > + P9Req *req;
> > +
> > + uint32_t body_size = 4 + 4;
> > + uint16_t string_size = v9fs_string_size(name);
> > +
> > + g_assert_cmpint(body_size, <=, UINT32_MAX - string_size);
> > + body_size += string_size;
> > +
> > + req = v9fs_req_init(v9p, body_size, P9_TLINK, tag);
> > + v9fs_uint32_write(req, dfid);
> > + v9fs_uint32_write(req, fid);
> > + v9fs_string_write(req, name);
> > + v9fs_req_send(req);
> > + return req;
> > +}
> > +
> > +/* size[4] Rlink tag[2] */
> > +static void v9fs_rlink(P9Req *req)
> > +{
> > + v9fs_req_recv(req, P9_RLINK);
> > + v9fs_req_free(req);
> > +}
> > +
> > /* size[4] Tunlinkat tag[2] dirfd[4] name[s] flags[4] */
> > static P9Req *v9fs_tunlinkat(QVirtio9P *v9p, uint32_t dirfd, const char
> > *name, uint32_t flags, uint16_t tag)
> > @@ -1142,6 +1170,21 @@ static void do_symlink(QVirtio9P *v9p, const char
> > *path, const char *clink, g_free(name);
> > }
> >
> > +/* create a hard link named @a clink in directory @a path pointing to @a to
> > */ +static void do_hardlink(QVirtio9P *v9p, const char *path, const char
> > *clink, + const char *to)
> > +{
> > + uint32_t dfid, fid;
> > + P9Req *req;
> > +
> > + dfid = do_walk(v9p, path);
> > + fid = do_walk(v9p, to);
> > +
> > + req = v9fs_tlink(v9p, dfid, fid, clink, 0);
> > + v9fs_req_wait_for_reply(req, NULL);
> > + v9fs_rlink(req);
> > +}
> > +
> > static void do_unlinkat(QVirtio9P *v9p, const char *atpath, const char
> > *rpath, uint32_t flags)
> > {
> > @@ -1321,6 +1364,33 @@ static void fs_unlinkat_symlink(void *obj, void
> > *data, g_free(real_file);
> > }
> >
> > +static void fs_hardlink_file(void *obj, void *data, QGuestAllocator
> > *t_alloc) +{
> > + QVirtio9P *v9p = obj;
> > + alloc = t_alloc;
> > + struct stat st_real, st_link;
> > + char *real_file = virtio_9p_test_path("07/real_file");
> > + char *hardlink_file = virtio_9p_test_path("07/hardlink_file");
> > +
> > + do_attach(v9p);
> > + do_mkdir(v9p, "/", "07");
> > + do_lcreate(v9p, "07", "real_file");
> > + g_assert(stat(real_file, &st_real) == 0);
> > + g_assert((st_real.st_mode & S_IFMT) == S_IFREG);
> > +
> > + do_hardlink(v9p, "07", "hardlink_file", "07/real_file");
> > +
> > + /* check if link exists now ... */
> > + g_assert(stat(hardlink_file, &st_link) == 0);
> > + /* ... and it's a hard link, right? */
> > + g_assert((st_link.st_mode & S_IFMT) == S_IFREG);
> > + g_assert(st_link.st_dev == st_real.st_dev);
> > + g_assert(st_link.st_ino == st_real.st_ino);
> > +
> > + g_free(hardlink_file);
> > + g_free(real_file);
> > +}
> > +
> > static void *assign_9p_local_driver(GString *cmd_line, void *arg)
> > {
> > virtio_9p_assign_local_driver(cmd_line, "security_model=mapped-xattr");
> > @@ -1367,6 +1437,7 @@ static void register_virtio_9p_test(void)
> > qos_add_test("local/symlink_file", "virtio-9p", fs_symlink_file,
> > &opts); qos_add_test("local/unlinkat_symlink", "virtio-9p",
> > fs_unlinkat_symlink, &opts);
> > + qos_add_test("local/hardlink_file", "virtio-9p", fs_hardlink_file,
> > &opts); }
> >
> > libqos_init(register_virtio_9p_test);
>
> Ok, I found the problem on the mentioned box that failed to create hard links
> with 9p: it is libvirt auto generating AppArmor policy rules for 9p export
> pathes, which libvirt generates with "rw" AA (AppArmor) permissions. Once I
> manually adjusted the AA rule to "rwl", creating hard links worked again.
>
> I guess I'll send a patch for libvirt to change that. At least IMO creating
> hard links with 9pfs is a very basic operation and should be enabled for the
> respective 9p export path by default.
>
> Actually I think it should also include "k" which means "file locking", as
> file locking is also a fundamental operation with 9pfs, right?
>
Well, I don't know exactly why libvirt is generating a strict AppArmor policy
but I'm not that surprised. If the user can _easily_ change the policy to
fit its needs, it's fine to have a "better safe than sorry" default.
> Best regards,
> Christian Schoenebeck
>
>
