vfs: Update mount API docs

 (4) Filesystem context security.

 (5) VFS filesystem context operations.

 (5) VFS filesystem context API.

 (6) Parameter description.

 (6) Superblock creation helpers.

 (7) Parameter helper functions.

 (7) Parameter description.

 (8) Parameter helper functions.

========

 (7) Destroy the context.

To support this, the file_system_type struct gains a new field:

To support this, the file_system_type struct gains two new fields:

	int (*init_fs_context)(struct fs_context *fc);

	const struct fs_parameter_description *parameters;

which is invoked to set up the filesystem-specific parts of a filesystem

context, including the additional space.

The first is invoked to set up the filesystem-specific parts of a filesystem

context, including the additional space, and the second points to the

parameter description for validation at registration time and querying by a

future system call.

Note that security initialisation is done *after* the filesystem is called so

that the namespaces may be adjusted first.

		void			*s_fs_info;

		unsigned int		sb_flags;

		unsigned int		sb_flags_mask;

		unsigned int		s_iflags;

		unsigned int		lsm_flags;

		enum fs_context_purpose	purpose:8;

		bool			sloppy:1;

		bool			silent:1;

		...

	};

     Which bits SB_* flags are to be set/cleared in super_block::s_flags.

 (*) unsigned int s_iflags

     These will be bitwise-OR'd with s->s_iflags when a superblock is created.

 (*) enum fs_context_purpose

     This indicates the purpose for which the context is intended.  The

	FS_CONTEXT_FOR_SUBMOUNT		-- New automatic submount of extant mount

	FS_CONTEXT_FOR_RECONFIGURE	-- Change an existing mount

 (*) bool sloppy

 (*) bool silent

     These are set if the sloppy or silent mount options are given.

     [NOTE] sloppy is probably unnecessary when userspace passes over one

     option at a time since the error can just be ignored if userspace deems it

     to be unimportant.

     [NOTE] silent is probably redundant with sb_flags & SB_SILENT.

The mount context is created by calling vfs_new_fs_context() or

vfs_dup_fs_context() and is destroyed with put_fs_context().  Note that the

structure is not refcounted.

     It should return 0 on success or a negative error code on failure.

=================================

VFS FILESYSTEM CONTEXT OPERATIONS

=================================

==========================

VFS FILESYSTEM CONTEXT API

==========================

There are four operations for creating a filesystem context and

one for destroying a context:

There are four operations for creating a filesystem context and one for

destroying a context:

 (*) struct fs_context *vfs_new_fs_context(struct file_system_type *fs_type,

					   struct dentry *reference,

 (*) struct fs_context *fs_context_for_mount(

		struct file_system_type *fs_type,

		unsigned int sb_flags);

     Allocate a filesystem context for the purpose of setting up a new mount,

     whether that be with a new superblock or sharing an existing one.  This

     sets the superblock flags, initialises the security and calls

     fs_type->init_fs_context() to initialise the filesystem private data.

     fs_type specifies the filesystem type that will manage the context and

     sb_flags presets the superblock flags stored therein.

 (*) struct fs_context *fs_context_for_reconfigure(

		struct dentry *dentry,

		unsigned int sb_flags,

					   unsigned int sb_flags_mask,

					   enum fs_context_purpose purpose);

		unsigned int sb_flags_mask);

     Allocate a filesystem context for the purpose of reconfiguring an

     existing superblock.  dentry provides a reference to the superblock to be

     configured.  sb_flags and sb_flags_mask indicate which superblock flags

     need changing and to what.

 (*) struct fs_context *fs_context_for_submount(

		struct file_system_type *fs_type,

		struct dentry *reference);

     Create a filesystem context for a given filesystem type and purpose.  This

     allocates the filesystem context, sets the superblock flags, initialises

     the security and calls fs_type->init_fs_context() to initialise the

     filesystem private data.

     Allocate a filesystem context for the purpose of creating a new mount for

     an automount point or other derived superblock.  fs_type specifies the

     filesystem type that will manage the context and the reference dentry

     supplies the parameters.  Namespaces are propagated from the reference

     dentry's superblock also.

     reference can be NULL or it may indicate the root dentry of a superblock

     that is going to be reconfigured (FS_CONTEXT_FOR_RECONFIGURE) or

     the automount point that triggered a submount (FS_CONTEXT_FOR_SUBMOUNT).

     This is provided as a source of namespace information.

     Note that it's not a requirement that the reference dentry be of the same

     filesystem type as fs_type.

 (*) struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc);

For the remaining operations, if an error occurs, a negative error code will be

returned.

 (*) int vfs_get_tree(struct fs_context *fc);

     Get or create the mountable root and superblock, using the parameters in

     the filesystem context to select/configure the superblock.  This invokes

     the ->validate() op and then the ->get_tree() op.

     [NOTE] ->validate() could perhaps be rolled into ->get_tree() and

     ->reconfigure().

 (*) struct vfsmount *vfs_create_mount(struct fs_context *fc);

     Create a mount given the parameters in the specified filesystem context.

     Note that this does not attach the mount to anything.

 (*) int vfs_parse_fs_param(struct fs_context *fc,

			    struct fs_parameter *param);

     clear the pointer, but then becomes responsible for disposing of the

     object.

 (*) int vfs_parse_fs_string(struct fs_context *fc, char *key,

 (*) int vfs_parse_fs_string(struct fs_context *fc, const char *key,

			     const char *value, size_t v_size);

     A wrapper around vfs_parse_fs_param() that just passes a constant string.

     A wrapper around vfs_parse_fs_param() that copies the value string it is

     passed.

 (*) int generic_parse_monolithic(struct fs_context *fc, void *data);

     Parse a sys_mount() data page, assuming the form to be a text list

     consisting of key[=val] options separated by commas.  Each item in the

     list is passed to vfs_mount_option().  This is the default when the

     ->parse_monolithic() operation is NULL.

     ->parse_monolithic() method is NULL.

 (*) int vfs_get_tree(struct fs_context *fc);

     Get or create the mountable root and superblock, using the parameters in

     the filesystem context to select/configure the superblock.  This invokes

     the ->get_tree() method.

 (*) struct vfsmount *vfs_create_mount(struct fs_context *fc);

     Create a mount given the parameters in the specified filesystem context.

     Note that this does not attach the mount to anything.

===========================

SUPERBLOCK CREATION HELPERS

===========================

A number of VFS helpers are available for use by filesystems for the creation

or looking up of superblocks.

 (*) struct super_block *

     sget_fc(struct fs_context *fc,

	     int (*test)(struct super_block *sb, struct fs_context *fc),

	     int (*set)(struct super_block *sb, struct fs_context *fc));

     This is the core routine.  If test is non-NULL, it searches for an

     existing superblock matching the criteria held in the fs_context, using

     the test function to match them.  If no match is found, a new superblock

     is created and the set function is called to set it up.

     Prior to the set function being called, fc->s_fs_info will be transferred

     to sb->s_fs_info - and fc->s_fs_info will be cleared if set returns

     success (ie. 0).

The following helpers all wrap sget_fc():

 (*) int vfs_get_super(struct fs_context *fc,

		       enum vfs_get_super_keying keying,

		       int (*fill_super)(struct super_block *sb,

					 struct fs_context *fc))

     This creates/looks up a deviceless superblock.  The keying indicates how

     many superblocks of this type may exist and in what manner they may be

     shared:

	(1) vfs_get_single_super

	    Only one such superblock may exist in the system.  Any further

	    attempt to get a new superblock gets this one (and any parameter

	    differences are ignored).

	(2) vfs_get_keyed_super

	    Multiple superblocks of this type may exist and they're keyed on

	    their s_fs_info pointer (for example this may refer to a

	    namespace).

	(3) vfs_get_independent_super

	    Multiple independent superblocks of this type may exist.  This

	    function never matches an existing one and always creates a new

	    one.

=====================

	struct fs_parameter_description {

		const char	name[16];

		u8		nr_params;

		u8		nr_alt_keys;

		u8		nr_enums;

		bool		ignore_unknown;

		bool		no_source;

		const char *const *keys;

		const struct constant_table *alt_keys;

		const struct fs_parameter_spec *specs;

		const struct fs_parameter_enum *enums;

	};

For example:

	enum afs_param {

	enum {

		Opt_autocell,

		Opt_bar,

		Opt_dyn,

		Opt_foo,

		Opt_source,

		nr__afs_params

	};

	static const struct fs_parameter_description afs_fs_parameters = {

		.name		= "kAFS",

		.nr_params	= nr__afs_params,

		.nr_alt_keys	= ARRAY_SIZE(afs_param_alt_keys),

		.nr_enums	= ARRAY_SIZE(afs_param_enums),

		.keys		= afs_param_keys,

		.alt_keys	= afs_param_alt_keys,

		.specs		= afs_param_specs,

		.enums		= afs_param_enums,

	};

     The name to be used in error messages generated by the parse helper

     functions.

 (2) u8 nr_params;

 (2) const struct fs_parameter_specification *specs;

     The number of discrete parameter identifiers.  This indicates the number

     of elements in the ->types[] array and also limits the values that may be

     used in the values that the ->keys[] array maps to.

     Table of parameter specifications, terminated with a null entry, where the

     entries are of type:

     It is expected that, for example, two parameters that are related, say

     "acl" and "noacl" with have the same ID, but will be flagged to indicate

     that one is the inverse of the other.  The value can then be picked out

     from the parse result.

 (3) const struct fs_parameter_specification *specs;

     Table of parameter specifications, where the entries are of type:

	struct fs_parameter_type {

		enum fs_parameter_spec	type:8;

		u8			flags;

	struct fs_parameter_spec {

		const char		*name;

		u8			opt;

		enum fs_parameter_type	type:8;

		unsigned short		flags;

	};

     and the parameter identifier is the index to the array.  'type' indicates

     the desired value type and must be one of:

     The 'name' field is a string to match exactly to the parameter key (no

     wildcards, patterns and no case-independence) and 'opt' is the value that

     will be returned by the fs_parser() function in the case of a successful

     match.

     The 'type' field indicates the desired value type and must be one of:

	TYPE NAME		EXPECTED VALUE		RESULT IN

	=======================	=======================	=====================

	fs_param_is_u32_octal	32-bit octal int	result->uint_32

	fs_param_is_u32_hex	32-bit hex int		result->uint_32

	fs_param_is_s32		32-bit signed int	result->int_32

	fs_param_is_u64		64-bit unsigned int	result->uint_64

	fs_param_is_enum	Enum value name 	result->uint_32

	fs_param_is_string	Arbitrary string	param->string

	fs_param_is_blob	Binary blob		param->blob

	fs_param_is_blockdev	Blockdev path		* Needs lookup

	fs_param_is_path	Path			* Needs lookup

	fs_param_is_fd		File descriptor		param->file

     And each parameter can be qualified with 'flags':

     	fs_param_v_optional	The value is optional

	fs_param_neg_with_no	If key name is prefixed with "no", it is false

	fs_param_neg_with_empty	If value is "", it is false

	fs_param_deprecated	The parameter is deprecated.

     For example:

	static const struct fs_parameter_spec afs_param_specs[nr__afs_params] = {

		[Opt_autocell]	= { fs_param_is flag },

		[Opt_bar]	= { fs_param_is_enum },

		[Opt_dyn]	= { fs_param_is flag },

		[Opt_foo]	= { fs_param_is_bool, fs_param_neg_with_no },

		[Opt_source]	= { fs_param_is_string },

	};

	fs_param_is_fd		File descriptor		result->int_32

     Note that if the value is of fs_param_is_bool type, fs_parse() will try

     to match any string value against "0", "1", "no", "yes", "false", "true".

     [!] NOTE that the table must be sorted according to primary key name so

     	 that ->keys[] is also sorted.

 (4) const char *const *keys;

     Table of primary key names for the parameters.  There must be one entry

     per defined parameter.  The table is optional if ->nr_params is 0.  The

     table is just an array of names e.g.:

	static const char *const afs_param_keys[nr__afs_params] = {

		[Opt_autocell]	= "autocell",

		[Opt_bar]	= "bar",

		[Opt_dyn]	= "dyn",

		[Opt_foo]	= "foo",

		[Opt_source]	= "source",

	};

     Each parameter can also be qualified with 'flags':

     [!] NOTE that the table must be sorted such that the table can be searched

     	 with bsearch() using strcmp().  This means that the Opt_* values must

     	 correspond to the entries in this table.

 (5) const struct constant_table *alt_keys;

     u8 nr_alt_keys;

     Table of additional key names and their mappings to parameter ID plus the

     number of elements in the table.  This is optional.  The table is just an

     array of { name, integer } pairs, e.g.:

	fs_param_v_optional	The value is optional

	fs_param_neg_with_no	result->negated set if key is prefixed with "no"

	fs_param_neg_with_empty	result->negated set if value is ""

	fs_param_deprecated	The parameter is deprecated.

	static const struct constant_table afs_param_keys[] = {

		{ "baz",	Opt_bar },

		{ "dynamic",	Opt_dyn },

     These are wrapped with a number of convenience wrappers:

	MACRO			SPECIFIES

	=======================	===============================================

	fsparam_flag()		fs_param_is_flag

	fsparam_flag_no()	fs_param_is_flag, fs_param_neg_with_no

	fsparam_bool()		fs_param_is_bool

	fsparam_u32()		fs_param_is_u32

	fsparam_u32oct()	fs_param_is_u32_octal

	fsparam_u32hex()	fs_param_is_u32_hex

	fsparam_s32()		fs_param_is_s32

	fsparam_u64()		fs_param_is_u64

	fsparam_enum()		fs_param_is_enum

	fsparam_string()	fs_param_is_string

	fsparam_blob()		fs_param_is_blob

	fsparam_bdev()		fs_param_is_blockdev

	fsparam_path()		fs_param_is_path

	fsparam_fd()		fs_param_is_fd

     all of which take two arguments, name string and option number - for

     example:

	static const struct fs_parameter_spec afs_param_specs[] = {

		fsparam_flag	("autocell",	Opt_autocell),

		fsparam_flag	("dyn",		Opt_dyn),

		fsparam_string	("source",	Opt_source),

		fsparam_flag_no	("foo",		Opt_foo),

		{}

	};

     [!] NOTE that the table must be sorted such that strcmp() can be used with

     	 bsearch() to search the entries.

     The parameter ID can also be fs_param_key_removed to indicate that a

     deprecated parameter has been removed and that an error will be given.

     This differs from fs_param_deprecated where the parameter may still have

     an effect.

     Further, the behaviour of the parameter may differ when an alternate name

     is used (for instance with NFS, "v3", "v4.2", etc. are alternate names).

     An addition macro, __fsparam() is provided that takes an additional pair

     of arguments to specify the type and the flags for anything that doesn't

     match one of the above macros.

 (6) const struct fs_parameter_enum *enums;

     u8 nr_enums;

     Table of enum value names to integer mappings and the number of elements

     stored therein.  This is of type:

     Table of enum value names to integer mappings, terminated with a null

     entry.  This is of type:

	struct fs_parameter_enum {

		u8		param_id;

		u8		opt;

		char		name[14];

		u8		value;

	};

     try to look the value up in the enum table and the result will be stored

     in the parse result.

 (7) bool no_source;

     If this is set, fs_parse() will ignore any "source" parameter and not

     pass it to the filesystem.

The parser should be pointed to by the parser pointer in the file_system_type

struct as this will provide validation on registration (if

CONFIG_VALIDATE_FS_PARSER=y) and will allow the description to be queried from

		int		value;

	};

     and it must be sorted such that it can be searched using bsearch() using

     strcmp().  If a match is found, the corresponding value is returned.  If a

     match isn't found, the not_found value is returned instead.

     If a match is found, the corresponding value is returned.  If a match

     isn't found, the not_found value is returned instead.

 (*) bool validate_constant_table(const struct constant_table *tbl,

				  size_t tbl_size,

     should just be set to lie inside the low-to-high range.

     If all is good, true is returned.  If the table is invalid, errors are

     logged to dmesg, the stack is dumped and false is returned.

     logged to dmesg and false is returned.

 (*) bool fs_validate_description(const struct fs_parameter_description *desc);

     This performs some validation checks on a parameter description.  It

     returns true if the description is good and false if it is not.  It will

     log errors to dmesg if validation fails.

 (*) int fs_parse(struct fs_context *fc,

		  const struct fs_param_parser *parser,

		  const struct fs_parameter_description *desc,

		  struct fs_parameter *param,

		  struct fs_param_parse_result *result);

		  struct fs_parse_result *result);

     This is the main interpreter of parameters.  It uses the parameter

     description (parser) to look up the name of the parameter to use and to

     convert that to a parameter ID (stored in result->key).

     description to look up a parameter by key name and to convert that to an

     option number (which it returns).

     If successful, and if the parameter type indicates the result is a

     boolean, integer or enum type, the value is converted by this function and

     the result stored in result->{boolean,int_32,uint_32}.

     the result stored in result->{boolean,int_32,uint_32,uint_64}.

     If a match isn't initially made, the key is prefixed with "no" and no

     value is present then an attempt will be made to look up the key with the

     prefix removed.  If this matches a parameter for which the type has flag

     fs_param_neg_with_no set, then a match will be made and the value will be

     set to false/0/NULL.

     If the parameter is successfully matched and, optionally, parsed

     correctly, 1 is returned.  If the parameter isn't matched and

     parser->ignore_unknown is set, then 0 is returned.  Otherwise -EINVAL is

     returned.

 (*) bool fs_validate_description(const struct fs_parameter_description *desc);

     fs_param_neg_with_no set, then a match will be made and result->negated

     will be set to true.

     This is validates the parameter description.  It returns true if the

     description is good and false if it is not.

     If the parameter isn't matched, -ENOPARAM will be returned; if the

     parameter is matched, but the value is erroneous, -EINVAL will be

     returned; otherwise the parameter's option number will be returned.

 (*) int fs_lookup_param(struct fs_context *fc,

			 struct fs_parameter *value,