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

[Luis Henriques <lhenriques@suse.de>]

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.

> + 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?

> +	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?

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
>