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

[Greg Kurz <groug@kaod.org>]

On Wed, 21 Oct 2020 20:20:08 +0200
Christian Schoenebeck <qemu_oss@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_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?
> 

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
> 
>