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Date:   Wed, 29 Jan 2020 01:23:06 +0800
From:   Gao Xiang <hsiangkao@aol.com>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Chao Yu <yuchao0@huawei.com>, dhowells@redhat.com,
        linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] erofs: convert to use the new mount fs_context api
Message-ID: <20200128172304.GA7941@hsiangkao-HP-ZHAN-66-Pro-G1>
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Hello Al,

Would you mind consider taking this patch into your working branch as well?
And we could avoid legacy mount API since 5.6...

Thank you very much,
Gao Xiang

On Thu, Jan 02, 2020 at 05:25:56PM +0800, Chao Yu wrote:
> Convert the erofs to use new internal mount API as the old one will
> be obsoleted and removed.  This allows greater flexibility in
> communication of mount parameters between userspace, the VFS and the
> filesystem.
> 
> See Documentation/filesystems/mount_api.txt for more information.
> 
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: David Howells <dhowells@redhat.com>
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
> ---
> v3:
> - if acl or xattr feature is not supported in erofs, change error msg
> a bit to indicate {,no}acl or {,no}user_xattr options are not supported.
> 
>  fs/erofs/internal.h |   2 +-
>  fs/erofs/super.c    | 233 +++++++++++++++++++-------------------------
>  2 files changed, 101 insertions(+), 134 deletions(-)
> 
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 1ed5beff7d11..a5fac25db6af 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -102,13 +102,13 @@ struct erofs_sb_info {
>  #define set_opt(sbi, option)	((sbi)->mount_opt |= EROFS_MOUNT_##option)
>  #define test_opt(sbi, option)	((sbi)->mount_opt & EROFS_MOUNT_##option)
>  
> -#ifdef CONFIG_EROFS_FS_ZIP
>  enum {
>  	EROFS_ZIP_CACHE_DISABLED,
>  	EROFS_ZIP_CACHE_READAHEAD,
>  	EROFS_ZIP_CACHE_READAROUND
>  };
>  
> +#ifdef CONFIG_EROFS_FS_ZIP
>  #define EROFS_LOCKED_MAGIC     (INT_MIN | 0xE0F510CCL)
>  
>  /* basic unit of the workstation of a super_block */
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 057e6d7b5b7f..388e6b34c736 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -10,6 +10,8 @@
>  #include <linux/parser.h>
>  #include <linux/seq_file.h>
>  #include <linux/crc32c.h>
> +#include <linux/fs_context.h>
> +#include <linux/fs_parser.h>
>  #include "xattr.h"
>  
>  #define CREATE_TRACE_POINTS
> @@ -192,41 +194,6 @@ static int erofs_read_superblock(struct super_block *sb)
>  	return ret;
>  }
>  
> -#ifdef CONFIG_EROFS_FS_ZIP
> -static int erofs_build_cache_strategy(struct super_block *sb,
> -				      substring_t *args)
> -{
> -	struct erofs_sb_info *sbi = EROFS_SB(sb);
> -	const char *cs = match_strdup(args);
> -	int err = 0;
> -
> -	if (!cs) {
> -		erofs_err(sb, "Not enough memory to store cache strategy");
> -		return -ENOMEM;
> -	}
> -
> -	if (!strcmp(cs, "disabled")) {
> -		sbi->cache_strategy = EROFS_ZIP_CACHE_DISABLED;
> -	} else if (!strcmp(cs, "readahead")) {
> -		sbi->cache_strategy = EROFS_ZIP_CACHE_READAHEAD;
> -	} else if (!strcmp(cs, "readaround")) {
> -		sbi->cache_strategy = EROFS_ZIP_CACHE_READAROUND;
> -	} else {
> -		erofs_err(sb, "Unrecognized cache strategy \"%s\"", cs);
> -		err = -EINVAL;
> -	}
> -	kfree(cs);
> -	return err;
> -}
> -#else
> -static int erofs_build_cache_strategy(struct super_block *sb,
> -				      substring_t *args)
> -{
> -	erofs_info(sb, "EROFS compression is disabled, so cache strategy is ignored");
> -	return 0;
> -}
> -#endif
> -
>  /* set up default EROFS parameters */
>  static void erofs_default_options(struct erofs_sb_info *sbi)
>  {
> @@ -251,73 +218,61 @@ enum {
>  	Opt_err
>  };
>  
> -static match_table_t erofs_tokens = {
> -	{Opt_user_xattr, "user_xattr"},
> -	{Opt_nouser_xattr, "nouser_xattr"},
> -	{Opt_acl, "acl"},
> -	{Opt_noacl, "noacl"},
> -	{Opt_cache_strategy, "cache_strategy=%s"},
> -	{Opt_err, NULL}
> +static const struct constant_table erofs_param_cache_strategy[] = {
> +	{"disabled",	EROFS_ZIP_CACHE_DISABLED},
> +	{"readahead",	EROFS_ZIP_CACHE_READAHEAD},
> +	{"readaround",	EROFS_ZIP_CACHE_READAROUND},
>  };
>  
> -static int erofs_parse_options(struct super_block *sb, char *options)
> -{
> -	substring_t args[MAX_OPT_ARGS];
> -	char *p;
> -	int err;
> -
> -	if (!options)
> -		return 0;
> -
> -	while ((p = strsep(&options, ","))) {
> -		int token;
> +static const struct fs_parameter_spec erofs_fs_parameters[] = {
> +	fsparam_flag_no("user_xattr",	Opt_user_xattr),
> +	fsparam_flag_no("acl",		Opt_acl),
> +	fsparam_enum("cache_strategy",	Opt_cache_strategy,
> +		     erofs_param_cache_strategy),
> +	{}
> +};
>  
> -		if (!*p)
> -			continue;
> +static int erofs_fc_parse_param(struct fs_context *fc,
> +				struct fs_parameter *param)
> +{
> +	struct erofs_sb_info *sbi __maybe_unused = fc->s_fs_info;
> +	struct fs_parse_result result;
> +	int opt;
>  
> -		args[0].to = args[0].from = NULL;
> -		token = match_token(p, erofs_tokens, args);
> +	opt = fs_parse(fc, erofs_fs_parameters, param, &result);
> +	if (opt < 0)
> +		return opt;
>  
> -		switch (token) {
> +	switch (opt) {
> +	case Opt_user_xattr:
>  #ifdef CONFIG_EROFS_FS_XATTR
> -		case Opt_user_xattr:
> -			set_opt(EROFS_SB(sb), XATTR_USER);
> -			break;
> -		case Opt_nouser_xattr:
> -			clear_opt(EROFS_SB(sb), XATTR_USER);
> -			break;
> +		if (result.boolean)
> +			set_opt(sbi, XATTR_USER);
> +		else
> +			clear_opt(sbi, XATTR_USER);
>  #else
> -		case Opt_user_xattr:
> -			erofs_info(sb, "user_xattr options not supported");
> -			break;
> -		case Opt_nouser_xattr:
> -			erofs_info(sb, "nouser_xattr options not supported");
> -			break;
> +		errorfc(fc, "{,no}user_xattr options not supported");
>  #endif
> +		break;
> +	case Opt_acl:
>  #ifdef CONFIG_EROFS_FS_POSIX_ACL
> -		case Opt_acl:
> -			set_opt(EROFS_SB(sb), POSIX_ACL);
> -			break;
> -		case Opt_noacl:
> -			clear_opt(EROFS_SB(sb), POSIX_ACL);
> -			break;
> +		if (result.boolean)
> +			set_opt(sbi, POSIX_ACL);
> +		else
> +			clear_opt(sbi, POSIX_ACL);
> +#else
> +		errorfc(fc, "{,no}acl options not supported");
> +#endif
> +		break;
> +	case Opt_cache_strategy:
> +#ifdef CONFIG_EROFS_FS_ZIP
> +		sbi->cache_strategy = result.uint_32;
>  #else
> -		case Opt_acl:
> -			erofs_info(sb, "acl options not supported");
> -			break;
> -		case Opt_noacl:
> -			erofs_info(sb, "noacl options not supported");
> -			break;
> +		errorfc(fc, "compression not supported, cache_strategy ignored");
>  #endif
> -		case Opt_cache_strategy:
> -			err = erofs_build_cache_strategy(sb, args);
> -			if (err)
> -				return err;
> -			break;
> -		default:
> -			erofs_err(sb, "Unrecognized mount option \"%s\" or missing value", p);
> -			return -EINVAL;
> -		}
> +		break;
> +	default:
> +		return -ENOPARAM;
>  	}
>  	return 0;
>  }
> @@ -381,7 +336,7 @@ static int erofs_init_managed_cache(struct super_block *sb)
>  static int erofs_init_managed_cache(struct super_block *sb) { return 0; }
>  #endif
>  
> -static int erofs_fill_super(struct super_block *sb, void *data, int silent)
> +static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  {
>  	struct inode *inode;
>  	struct erofs_sb_info *sbi;
> @@ -394,11 +349,7 @@ static int erofs_fill_super(struct super_block *sb, void *data, int silent)
>  		return -EINVAL;
>  	}
>  
> -	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> -	if (!sbi)
> -		return -ENOMEM;
> -
> -	sb->s_fs_info = sbi;
> +	sbi = sb->s_fs_info;
>  	err = erofs_read_superblock(sb);
>  	if (err)
>  		return err;
> @@ -412,12 +363,6 @@ static int erofs_fill_super(struct super_block *sb, void *data, int silent)
>  #ifdef CONFIG_EROFS_FS_XATTR
>  	sb->s_xattr = erofs_xattr_handlers;
>  #endif
> -	/* set erofs default mount options */
> -	erofs_default_options(sbi);
> -
> -	err = erofs_parse_options(sb, data);
> -	if (err)
> -		return err;
>  
>  	if (test_opt(sbi, POSIX_ACL))
>  		sb->s_flags |= SB_POSIXACL;
> @@ -450,15 +395,61 @@ static int erofs_fill_super(struct super_block *sb, void *data, int silent)
>  	if (err)
>  		return err;
>  
> -	erofs_info(sb, "mounted with opts: %s, root inode @ nid %llu.",
> -		   (char *)data, ROOT_NID(sbi));
> +	erofs_info(sb, "mounted with root inode @ nid %llu.", ROOT_NID(sbi));
> +	return 0;
> +}
> +
> +static int erofs_fc_get_tree(struct fs_context *fc)
> +{
> +	return get_tree_bdev(fc, erofs_fc_fill_super);
> +}
> +
> +static int erofs_fc_reconfigure(struct fs_context *fc)
> +{
> +	struct super_block *sb = fc->root->d_sb;
> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
> +
> +	DBG_BUGON(!sb_rdonly(sb));
> +
> +	if (test_opt(sbi, POSIX_ACL))
> +		fc->sb_flags |= SB_POSIXACL;
> +	else
> +		fc->sb_flags &= ~SB_POSIXACL;
> +
> +	fc->sb_flags |= SB_RDONLY;
>  	return 0;
>  }
>  
> -static struct dentry *erofs_mount(struct file_system_type *fs_type, int flags,
> -				  const char *dev_name, void *data)
> +static void erofs_fc_free(struct fs_context *fc)
>  {
> -	return mount_bdev(fs_type, flags, dev_name, data, erofs_fill_super);
> +	/*
> +	 * sbi stored in fs_context was cleaned after transferring
> +	 * to corresponding superblock on a successful new mount,
> +	 * or free it here.
> +	 */
> +	kfree(fc->s_fs_info);
> +}
> +
> +static const struct fs_context_operations erofs_context_ops = {
> +	.parse_param	= erofs_fc_parse_param,
> +	.get_tree       = erofs_fc_get_tree,
> +	.reconfigure    = erofs_fc_reconfigure,
> +	.free		= erofs_fc_free,
> +};
> +
> +static int erofs_init_fs_context(struct fs_context *fc)
> +{
> +	struct erofs_sb_info *sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> +
> +	if (!sbi)
> +		return -ENOMEM;
> +
> +	/* set default mount options */
> +	erofs_default_options(sbi);
> +
> +	fc->s_fs_info = sbi;
> +	fc->ops = &erofs_context_ops;
> +	return 0;
>  }
>  
>  /*
> @@ -497,7 +488,7 @@ static void erofs_put_super(struct super_block *sb)
>  static struct file_system_type erofs_fs_type = {
>  	.owner          = THIS_MODULE,
>  	.name           = "erofs",
> -	.mount          = erofs_mount,
> +	.init_fs_context = erofs_init_fs_context,
>  	.kill_sb        = erofs_kill_sb,
>  	.fs_flags       = FS_REQUIRES_DEV,
>  };
> @@ -603,36 +594,12 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
>  	return 0;
>  }
>  
> -static int erofs_remount(struct super_block *sb, int *flags, char *data)
> -{
> -	struct erofs_sb_info *sbi = EROFS_SB(sb);
> -	unsigned int org_mnt_opt = sbi->mount_opt;
> -	int err;
> -
> -	DBG_BUGON(!sb_rdonly(sb));
> -	err = erofs_parse_options(sb, data);
> -	if (err)
> -		goto out;
> -
> -	if (test_opt(sbi, POSIX_ACL))
> -		sb->s_flags |= SB_POSIXACL;
> -	else
> -		sb->s_flags &= ~SB_POSIXACL;
> -
> -	*flags |= SB_RDONLY;
> -	return 0;
> -out:
> -	sbi->mount_opt = org_mnt_opt;
> -	return err;
> -}
> -
>  const struct super_operations erofs_sops = {
>  	.put_super = erofs_put_super,
>  	.alloc_inode = erofs_alloc_inode,
>  	.free_inode = erofs_free_inode,
>  	.statfs = erofs_statfs,
>  	.show_options = erofs_show_options,
> -	.remount_fs = erofs_remount,
>  };
>  
>  module_init(erofs_module_init);
> -- 
> 2.18.0.rc1
>