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Fixed MTP to work with TWRP
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awab228
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227
Documentation/filesystems/pohmelfs/network_protocol.txt
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227
Documentation/filesystems/pohmelfs/network_protocol.txt
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POHMELFS network protocol.
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Basic structure used in network communication is following command:
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struct netfs_cmd
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{
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__u16 cmd; /* Command number */
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__u16 csize; /* Attached crypto information size */
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__u16 cpad; /* Attached padding size */
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__u16 ext; /* External flags */
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__u32 size; /* Size of the attached data */
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__u32 trans; /* Transaction id */
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__u64 id; /* Object ID to operate on. Used for feedback.*/
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__u64 start; /* Start of the object. */
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__u64 iv; /* IV sequence */
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__u8 data[0];
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};
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Commands can be embedded into transaction command (which in turn has own command),
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so one can extend protocol as needed without breaking backward compatibility as long
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as old commands are supported. All string lengths include tail 0 byte.
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All commands are transferred over the network in big-endian. CPU endianness is used at the end peers.
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@cmd - command number, which specifies command to be processed. Following
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commands are used currently:
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NETFS_READDIR = 1, /* Read directory for given inode number */
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NETFS_READ_PAGE, /* Read data page from the server */
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NETFS_WRITE_PAGE, /* Write data page to the server */
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NETFS_CREATE, /* Create directory entry */
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NETFS_REMOVE, /* Remove directory entry */
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NETFS_LOOKUP, /* Lookup single object */
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NETFS_LINK, /* Create a link */
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NETFS_TRANS, /* Transaction */
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NETFS_OPEN, /* Open intent */
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NETFS_INODE_INFO, /* Metadata cache coherency synchronization message */
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NETFS_PAGE_CACHE, /* Page cache invalidation message */
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NETFS_READ_PAGES, /* Read multiple contiguous pages in one go */
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NETFS_RENAME, /* Rename object */
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NETFS_CAPABILITIES, /* Capabilities of the client, for example supported crypto */
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NETFS_LOCK, /* Distributed lock message */
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NETFS_XATTR_SET, /* Set extended attribute */
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NETFS_XATTR_GET, /* Get extended attribute */
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@ext - external flags. Used by different commands to specify some extra arguments
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like partial size of the embedded objects or creation flags.
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@size - size of the attached data. For NETFS_READ_PAGE and NETFS_READ_PAGES no data is attached,
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but size of the requested data is incorporated here. It does not include size of the command
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header (struct netfs_cmd) itself.
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@id - id of the object this command operates on. Each command can use it for own purpose.
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@start - start of the object this command operates on. Each command can use it for own purpose.
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@csize, @cpad - size and padding size of the (attached if needed) crypto information.
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Command specifications.
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@NETFS_READDIR
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This command is used to sync content of the remote dir to the client.
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@ext - length of the path to object.
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@size - the same.
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@id - local inode number of the directory to read.
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@start - zero.
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@NETFS_READ_PAGE
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This command is used to read data from remote server.
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Data size does not exceed local page cache size.
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@id - inode number.
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@start - first byte offset.
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@size - number of bytes to read plus length of the path to object.
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@ext - object path length.
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@NETFS_CREATE
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Used to create object.
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It does not require that all directories on top of the object were
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already created, it will create them automatically. Each object has
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associated @netfs_path_entry data structure, which contains creation
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mode (permissions and type) and length of the name as long as name itself.
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@start - 0
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@size - size of the all data structures needed to create a path
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@id - local inode number
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@ext - 0
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@NETFS_REMOVE
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Used to remove object.
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@ext - length of the path to object.
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@size - the same.
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@id - local inode number.
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@start - zero.
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@NETFS_LOOKUP
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Lookup information about object on server.
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@ext - length of the path to object.
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@size - the same.
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@id - local inode number of the directory to look object in.
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@start - local inode number of the object to look at.
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@NETFS_LINK
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Create hard of symlink.
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Command is sent as "object_path|target_path".
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@size - size of the above string.
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@id - parent local inode number.
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@start - 1 for symlink, 0 for hardlink.
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@ext - size of the "object_path" above.
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@NETFS_TRANS
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Transaction header.
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@size - incorporates all embedded command sizes including theirs header sizes.
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@start - transaction generation number - unique id used to find transaction.
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@ext - transaction flags. Unused at the moment.
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@id - 0.
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@NETFS_OPEN
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Open intent for given transaction.
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@id - local inode number.
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@start - 0.
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@size - path length to the object.
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@ext - open flags (O_RDWR and so on).
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@NETFS_INODE_INFO
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Metadata update command.
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It is sent to servers when attributes of the object are changed and received
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when data or metadata were updated. It operates with the following structure:
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struct netfs_inode_info
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{
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unsigned int mode;
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unsigned int nlink;
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unsigned int uid;
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unsigned int gid;
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unsigned int blocksize;
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unsigned int padding;
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__u64 ino;
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__u64 blocks;
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__u64 rdev;
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__u64 size;
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__u64 version;
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};
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It effectively mirrors stat(2) returned data.
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@ext - path length to the object.
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@size - the same plus size of the netfs_inode_info structure.
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@id - local inode number.
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@start - 0.
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@NETFS_PAGE_CACHE
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Command is only received by clients. It contains information about
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page to be marked as not up-to-date.
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@id - client's inode number.
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@start - last byte of the page to be invalidated. If it is not equal to
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current inode size, it will be vmtruncated().
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@size - 0
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@ext - 0
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@NETFS_READ_PAGES
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Used to read multiple contiguous pages in one go.
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@start - first byte of the contiguous region to read.
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@size - contains of two fields: lower 8 bits are used to represent page cache shift
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used by client, another 3 bytes are used to get number of pages.
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@id - local inode number.
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@ext - path length to the object.
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@NETFS_RENAME
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Used to rename object.
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Attached data is formed into following string: "old_path|new_path".
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@id - local inode number.
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@start - parent inode number.
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@size - length of the above string.
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@ext - length of the old path part.
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@NETFS_CAPABILITIES
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Used to exchange crypto capabilities with server.
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If crypto capabilities are not supported by server, then client will disable it
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or fail (if 'crypto_fail_unsupported' mount options was specified).
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@id - superblock index. Used to specify crypto information for group of servers.
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@size - size of the attached capabilities structure.
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@start - 0.
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@size - 0.
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@scsize - 0.
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@NETFS_LOCK
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Used to send lock request/release messages. Although it sends byte range request
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and is capable of flushing pages based on that, it is not used, since all Linux
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filesystems lock the whole inode.
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@id - lock generation number.
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@start - start of the locked range.
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@size - size of the locked range.
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@ext - lock type: read/write. Not used actually. 15'th bit is used to determine,
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if it is lock request (1) or release (0).
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@NETFS_XATTR_SET
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@NETFS_XATTR_GET
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Used to set/get extended attributes for given inode.
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@id - attribute generation number or xattr setting type
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@start - size of the attribute (request or attached)
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@size - name length, path len and data size for given attribute
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@ext - path length for given object
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