Re: [PATCH v2 1/4] ceph: new device mount syntax

[Venky Shankar <vshankar@redhat.com>]

On Fri, Jul 2, 2021 at 4:08 PM Luis Henriques <lhenriques@suse.de> wrote:
>
> On Fri, Jul 02, 2021 at 12:18:18PM +0530, Venky Shankar wrote:
> > Old mount device syntax (source) has the following problems:
> >
> > - mounts to the same cluster but with different fsnames
> >   and/or creds have identical device string which can
> >   confuse xfstests.
> >
> > - Userspace mount helper tool resolves monitor addresses
> >   and fill in mon addrs automatically, but that means the
> >   device shown in /proc/mounts is different than what was
> >   used for mounting.
> >
> > New device syntax is as follows:
> >
> >   cephuser@fsid.mycephfs2=/path
> >
> > Note, there is no "monitor address" in the device string.
> > That gets passed in as mount option. This keeps the device
> > string same when monitor addresses change (on remounts).
> >
> > Also note that the userspace mount helper tool is backward
> > compatible. I.e., the mount helper will fallback to using
> > old syntax after trying to mount with the new syntax.
> >
> > Signed-off-by: Venky Shankar <vshankar@redhat.com>
> > ---
> >  fs/ceph/super.c | 122 ++++++++++++++++++++++++++++++++++++++++++++----
> >  fs/ceph/super.h |   3 ++
> >  2 files changed, 115 insertions(+), 10 deletions(-)
> >
> > diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> > index 9b1b7f4cfdd4..0b324e43c9f4 100644
> > --- a/fs/ceph/super.c
> > +++ b/fs/ceph/super.c
> > @@ -145,6 +145,7 @@ enum {
> >       Opt_mds_namespace,
> >       Opt_recover_session,
> >       Opt_source,
> > +     Opt_mon_addr,
> >       /* string args above */
> >       Opt_dirstat,
> >       Opt_rbytes,
> > @@ -196,6 +197,7 @@ static const struct fs_parameter_spec ceph_mount_parameters[] = {
> >       fsparam_u32     ("rsize",                       Opt_rsize),
> >       fsparam_string  ("snapdirname",                 Opt_snapdirname),
> >       fsparam_string  ("source",                      Opt_source),
> > +     fsparam_string  ("mon_addr",                    Opt_mon_addr),
> >       fsparam_u32     ("wsize",                       Opt_wsize),
> >       fsparam_flag_no ("wsync",                       Opt_wsync),
> >       {}
> > @@ -226,10 +228,70 @@ static void canonicalize_path(char *path)
> >       path[j] = '\0';
> >  }
> >
> > +static int ceph_parse_old_source(const char *dev_name, const char *dev_name_end,
> > +                              struct fs_context *fc)
> > +{
> > +     int r;
> > +     struct ceph_parse_opts_ctx *pctx = fc->fs_private;
> > +     struct ceph_mount_options *fsopt = pctx->opts;
> > +
> > +     if (*dev_name_end != ':')
> > +             return invalfc(fc, "separator ':' missing in source");
> > +
> > +     r = ceph_parse_mon_ips(dev_name, dev_name_end - dev_name,
> > +                            pctx->copts, fc->log.log);
> > +     if (r)
> > +             return r;
> > +
> > +     fsopt->new_dev_syntax = false;
> > +     return 0;
> > +}
> > +
> > +static int ceph_parse_new_source(const char *dev_name, const char *dev_name_end,
> > +                              struct fs_context *fc)
> > +{
> > +     struct ceph_parse_opts_ctx *pctx = fc->fs_private;
> > +     struct ceph_mount_options *fsopt = pctx->opts;
> > +     char *fsid_start, *fs_name_start;
> > +
> > +     if (*dev_name_end != '=') {
> > +             dout("separator '=' missing in source");
> > +             return -EINVAL;
> > +     }
> > +
> > +     fsid_start = strchr(dev_name, '@');
> > +     if (!fsid_start)
> > +             return invalfc(fc, "missing cluster fsid");
> > +     ++fsid_start; /* start of cluster fsid */
> > +
> > +     fs_name_start = strchr(fsid_start, '.');
> > +     if (!fs_name_start)
> > +             return invalfc(fc, "missing file system name");
> > +
> > +     ++fs_name_start; /* start of file system name */
> > +     fsopt->mds_namespace = kstrndup(fs_name_start,
> > +                                     dev_name_end - fs_name_start, GFP_KERNEL);
> > +     if (!fsopt->mds_namespace)
> > +             return -ENOMEM;
> > +     dout("file system (mds namespace) '%s'\n", fsopt->mds_namespace);
> > +
> > +     fsopt->new_dev_syntax = true;
> > +     return 0;
> > +}
> > +
> >  /*
> > - * Parse the source parameter.  Distinguish the server list from the path.
> > + * Parse the source parameter for new device format. Distinguish the device
> > + * spec from the path. Try parsing new device format and fallback to old
> > + * format if needed.
> >   *
> > - * The source will look like:
> > + * New device syntax will looks like:
> > + *     <device_spec>=/<path>
> > + * where
> > + *     <device_spec> is name@fsid.fsname
> > + *     <path> is optional, but if present must begin with '/'
> > + * (monitor addresses are passed via mount option)
> > + *
> > + * Old device syntax is:
> >   *     <server_spec>[,<server_spec>...]:[<path>]
> >   * where
> >   *     <server_spec> is <ip>[:<port>]
> > @@ -262,22 +324,48 @@ static int ceph_parse_source(struct fs_parameter *param, struct fs_context *fc)
> >               dev_name_end = dev_name + strlen(dev_name);
> >       }
> >
> > -     dev_name_end--;         /* back up to ':' separator */
> > -     if (dev_name_end < dev_name || *dev_name_end != ':')
> > -             return invalfc(fc, "No path or : separator in source");
> > +     dev_name_end--;         /* back up to separator */
> > +     if (dev_name_end < dev_name)
> > +             return invalfc(fc, "path missing in source");
> >
> >       dout("device name '%.*s'\n", (int)(dev_name_end - dev_name), dev_name);
> >       if (fsopt->server_path)
> >               dout("server path '%s'\n", fsopt->server_path);
> >
> > -     ret = ceph_parse_mon_ips(param->string, dev_name_end - dev_name,
> > -                              pctx->copts, fc->log.log);
> > +     dout("trying new device syntax");
> > +     ret = ceph_parse_new_source(dev_name, dev_name_end, fc);
> > +     if (ret == 0)
> > +             goto done;
> > +
> > +     dout("trying old device syntax");
> > +     ret = ceph_parse_old_source(dev_name, dev_name_end, fc);
> >       if (ret)
> > -             return ret;
> > +             goto out;
>
> Do we really need this goto?  My (personal) preference would be to drop
> this one and simply return.   And maybe it's even possible to drop the
> previous 'goto done' too.

Sure. Just a preference I had.

>
> > + done:
> >       fc->source = param->string;
> >       param->string = NULL;
> > -     return 0;
> > + out:
> > +     return ret;
> > +}
> > +
> > +static int ceph_parse_mon_addr(struct fs_parameter *param,
> > +                            struct fs_context *fc)
> > +{
> > +     int r;
> > +     struct ceph_parse_opts_ctx *pctx = fc->fs_private;
> > +     struct ceph_mount_options *fsopt = pctx->opts;
> > +
> > +     kfree(fsopt->mon_addr);
> > +     fsopt->mon_addr = param->string;
> > +     param->string = NULL;
> > +
> > +     strreplace(fsopt->mon_addr, '/', ',');
> > +     r = ceph_parse_mon_ips(fsopt->mon_addr, strlen(fsopt->mon_addr),
> > +                            pctx->copts, fc->log.log);
> > +        // since its used in ceph_show_options()
>
> (nit: use c-style comments...? yeah, again personal preference :-)
>
> > +     strreplace(fsopt->mon_addr, ',', '/');
>
> This is ugly.  Have you considered modifying ceph_parse_mon_ips() (and
> ceph_parse_ips()) to receive a delimiter as a parameter?''

I did. However, for most cases (all possibly), "," is the addr
delimiter. So, I didn't take the approach to make these helpers really
generic for parsing addrs.

>
> > +     return r;
> >  }
> >
> >  static int ceph_parse_mount_param(struct fs_context *fc,
> > @@ -322,6 +410,8 @@ static int ceph_parse_mount_param(struct fs_context *fc,
> >               if (fc->source)
> >                       return invalfc(fc, "Multiple sources specified");
> >               return ceph_parse_source(param, fc);
> > +     case Opt_mon_addr:
> > +             return ceph_parse_mon_addr(param, fc);
> >       case Opt_wsize:
> >               if (result.uint_32 < PAGE_SIZE ||
> >                   result.uint_32 > CEPH_MAX_WRITE_SIZE)
> > @@ -473,6 +563,7 @@ static void destroy_mount_options(struct ceph_mount_options *args)
> >       kfree(args->mds_namespace);
> >       kfree(args->server_path);
> >       kfree(args->fscache_uniq);
> > +     kfree(args->mon_addr);
> >       kfree(args);
> >  }
> >
> > @@ -516,6 +607,10 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
> >       if (ret)
> >               return ret;
> >
> > +     ret = strcmp_null(fsopt1->mon_addr, fsopt2->mon_addr);
> > +     if (ret)
> > +             return ret;
> > +
> >       return ceph_compare_options(new_opt, fsc->client);
> >  }
> >
> > @@ -571,9 +666,13 @@ static int ceph_show_options(struct seq_file *m, struct dentry *root)
> >       if ((fsopt->flags & CEPH_MOUNT_OPT_NOCOPYFROM) == 0)
> >               seq_puts(m, ",copyfrom");
> >
> > -     if (fsopt->mds_namespace)
> > +     /* dump mds_namespace when old device syntax is in use */
> > +     if (fsopt->mds_namespace && !fsopt->new_dev_syntax)
> >               seq_show_option(m, "mds_namespace", fsopt->mds_namespace);
>
> I haven't really tested it, but... what happens if we set mds_namespace
> *and* we're using the new syntax?  Or, in another words, what should
> happen?

Depends on the order of token parsing in ceph_parse_mount_param()
which mds_namespace gets used.

(however, that means ceph_parse_new_source() should additionally
kfree(fsopt->mds_namespace)).

>
> Cheers,
> --
> Luís
>
> >
> > +     if (fsopt->mon_addr)
> > +             seq_printf(m, ",mon_addr=%s", fsopt->mon_addr);
> > +
> >       if (fsopt->flags & CEPH_MOUNT_OPT_CLEANRECOVER)
> >               seq_show_option(m, "recover_session", "clean");
> >
> > @@ -1048,6 +1147,7 @@ static int ceph_setup_bdi(struct super_block *sb, struct ceph_fs_client *fsc)
> >  static int ceph_get_tree(struct fs_context *fc)
> >  {
> >       struct ceph_parse_opts_ctx *pctx = fc->fs_private;
> > +     struct ceph_mount_options *fsopt = pctx->opts;
> >       struct super_block *sb;
> >       struct ceph_fs_client *fsc;
> >       struct dentry *res;
> > @@ -1059,6 +1159,8 @@ static int ceph_get_tree(struct fs_context *fc)
> >
> >       if (!fc->source)
> >               return invalfc(fc, "No source");
> > +     if (fsopt->new_dev_syntax && !fsopt->mon_addr)
> > +             return invalfc(fc, "No monitor address");
> >
> >       /* create client (which we may/may not use) */
> >       fsc = create_fs_client(pctx->opts, pctx->copts);
> > diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> > index c48bb30c8d70..8f71184b7c85 100644
> > --- a/fs/ceph/super.h
> > +++ b/fs/ceph/super.h
> > @@ -87,6 +87,8 @@ struct ceph_mount_options {
> >       unsigned int max_readdir;       /* max readdir result (entries) */
> >       unsigned int max_readdir_bytes; /* max readdir result (bytes) */
> >
> > +     bool new_dev_syntax;
> > +
> >       /*
> >        * everything above this point can be memcmp'd; everything below
> >        * is handled in compare_mount_options()
> > @@ -96,6 +98,7 @@ struct ceph_mount_options {
> >       char *mds_namespace;  /* default NULL */
> >       char *server_path;    /* default NULL (means "/") */
> >       char *fscache_uniq;   /* default NULL */
> > +     char *mon_addr;
> >  };
> >
> >  struct ceph_fs_client {
> > --
> > 2.27.0
> >
>


-- 
Cheers,
Venky