Re: [PATCH v2 7/8] tests/9pfs: add local Tlink test

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

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_oss@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?

Best regards,
Christian Schoenebeck