Staging: pohmelfs: documentation.

This patch includes POHMELFS design and implementation description.
Separate file includes mount options, default parameters and usage examples.

Signed-off-by: Eveniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 227 insertions, 0 deletions

diff --git a/Documentation/filesystems/pohmelfs/network_protocol.txt b/Documentation/filesystems/pohmelfs/network_protocol.txt
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+POHMELFS network protocol.
+
+Basic structure used in network communication is following command:
+
+struct netfs_cmd
+{
+	__u16			cmd;	/* Command number */
+	__u16			csize;	/* Attached crypto information size */
+	__u16			cpad;	/* Attached padding size */
+	__u16			ext;	/* External flags */
+	__u32			size;	/* Size of the attached data */
+	__u32			trans;	/* Transaction id */
+	__u64			id;	/* Object ID to operate on. Used for feedback.*/
+	__u64			start;	/* Start of the object. */
+	__u64			iv;	/* IV sequence */
+	__u8			data[0];
+};
+
+Commands can be embedded into transaction command (which in turn has own command),
+so one can extend protocol as needed without breaking backward compatibility as long
+as old commands are supported. All string lengths include tail 0 byte.
+
+All commans are transfered over the network in big-endian. CPU endianess is used at the end peers.
+
+@cmd - command number, which specifies command to be processed. Following
+	commands are used currently:
+
+	NETFS_READDIR	= 1,	/* Read directory for given inode number */
+	NETFS_READ_PAGE,	/* Read data page from the server */
+	NETFS_WRITE_PAGE,	/* Write data page to the server */
+	NETFS_CREATE,		/* Create directory entry */
+	NETFS_REMOVE,		/* Remove directory entry */
+	NETFS_LOOKUP,		/* Lookup single object */
+	NETFS_LINK,		/* Create a link */
+	NETFS_TRANS,		/* Transaction */
+	NETFS_OPEN,		/* Open intent */
+	NETFS_INODE_INFO,	/* Metadata cache coherency synchronization message */
+	NETFS_PAGE_CACHE,	/* Page cache invalidation message */
+	NETFS_READ_PAGES,	/* Read multiple contiguous pages in one go */
+	NETFS_RENAME,		/* Rename object */
+	NETFS_CAPABILITIES,	/* Capabilities of the client, for example supported crypto */
+	NETFS_LOCK,		/* Distributed lock message */
+	NETFS_XATTR_SET,	/* Set extended attribute */
+	NETFS_XATTR_GET,	/* Get extended attribute */
+
+@ext - external flags. Used by different commands to specify some extra arguments
+	like partial size of the embedded objects or creation flags.
+
+@size - size of the attached data. For NETFS_READ_PAGE and NETFS_READ_PAGES no data is attached,
+	but size of the requested data is incorporated here. It does not include size of the command
+	header (struct netfs_cmd) itself.
+
+@id - id of the object this command operates on. Each command can use it for own purpose.
+
+@start - start of the object this command operates on. Each command can use it for own purpose.
+
+@csize, @cpad - size and padding size of the (attached if needed) crypto information.
+
+Command specifications.
+
+@NETFS_READDIR
+This command is used to sync content of the remote dir to the client.
+
+@ext - length of the path to object.
+@size - the same.
+@id - local inode number of the directory to read.
+@start - zero.
+
+
+@NETFS_READ_PAGE
+This command is used to read data from remote server.
+Data size does not exceed local page cache size.
+
+@id - inode number.
+@start - first byte offset.
+@size - number of bytes to read plus length of the path to object.
+@ext - object path length.
+
+
+@NETFS_CREATE
+Used to create object.
+It does not require that all directories on top of the object were
+already created, it will create them automatically. Each object has
+associated @netfs_path_entry data structure, which contains creation
+mode (permissions and type) and length of the name as long as name itself.
+
+@start - 0
+@size - size of the all data structures needed to create a path
+@id - local inode number
+@ext - 0
+
+
+@NETFS_REMOVE
+Used to remove object.
+
+@ext - length of the path to object.
+@size - the same.
+@id - local inode number.
+@start - zero.
+
+
+@NETFS_LOOKUP
+Lookup information about object on server.
+
+@ext - length of the path to object.
+@size - the same.
+@id - local inode number of the directory to look object in.
+@start - local inode number of the object to look at.
+
+
+@NETFS_LINK
+Create hard of symlink.
+Command is sent as "object_path|target_path".
+
+@size - size of the above string.
+@id - parent local inode number.
+@start - 1 for symlink, 0 for hardlink.
+@ext - size of the "object_path" above.
+
+
+@NETFS_TRANS
+Transaction header.
+
+@size - incorporates all embedded command sizes including theirs header sizes.
+@start - transaction generation number - unique id used to find transaction.
+@ext - transaction flags. Unused at the moment.
+@id - 0.
+
+
+@NETFS_OPEN
+Open intent for given transaction.
+
+@id - local inode number.
+@start - 0.
+@size - path length to the object.
+@ext - open flags (O_RDWR and so on).
+
+
+@NETFS_INODE_INFO
+Metadata update command.
+It is sent to servers when attributes of the object are changed and received
+when data or metadata were updated. It operates with the following structure:
+
+struct netfs_inode_info
+{
+	unsigned int		mode;
+	unsigned int		nlink;
+	unsigned int		uid;
+	unsigned int		gid;
+	unsigned int		blocksize;
+	unsigned int		padding;
+	__u64			ino;
+	__u64			blocks;
+	__u64			rdev;
+	__u64			size;
+	__u64			version;
+};
+
+It effectively mirrors stat(2) returned data.
+
+
+@ext - path length to the object.
+@size - the same plus size of the netfs_inode_info structure.
+@id - local inode number.
+@start - 0.
+
+
+@NETFS_PAGE_CACHE
+Command is only received by clients. It contains information about
+page to be marked as not up-to-date.
+
+@id - client's inode number.
+@start - last byte of the page to be invalidated. If it is not equal to
+	current inode size, it will be vmtruncated().
+@size - 0
+@ext - 0
+
+
+@NETFS_READ_PAGES
+Used to read multiple contiguous pages in one go.
+
+@start - first byte of the contiguous region to read.
+@size - contains of two fields: lower 8 bits are used to represent page cache shift
+	used by client, another 3 bytes are used to get number of pages.
+@id - local inode number.
+@ext - path length to the object.
+
+
+@NETFS_RENAME
+Used to rename object.
+Attached data is formed into following string: "old_path|new_path".
+
+@id - local inode number.
+@start - parent inode number.
+@size - length of the above string.
+@ext - length of the old path part.
+
+
+@NETFS_CAPABILITIES
+Used to exchange crypto capabilities with server.
+If crypto capabilities are not supported by server, then client will disable it
+or fail (if 'crypto_fail_unsupported' mount options was specified).
+
+@id - superblock index. Used to specify crypto information for group of servers.
+@size - size of the attached capabilities structure.
+@start - 0.
+@size - 0.
+@scsize - 0.
+
+@NETFS_LOCK
+Used to send lock request/release messages. Although it sends byte range request
+and is capable of flushing pages based on that, it is not used, since all Linux
+filesystems lock the whole inode.
+
+@id - lock generation number.
+@start - start of the locked range.
+@size - size of the locked range.
+@ext - lock type: read/write. Not used actually. 15'th bit is used to determine,
+	if it is lock request (1) or release (0).
+
+@NETFS_XATTR_SET
+@NETFS_XATTR_GET
+Used to set/get extended attributes for given inode.
+@id - attribute generation number or xattr setting type
+@start - size of the attribute (request or attached)
+@size - name length, path len and data size for given attribute
+@ext - path length for given object