Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 POHMELFS network protocol. 2 3 Basic structure used in network communication is following command: 4 5 struct netfs_cmd 6 { 7 __u16 cmd; /* Command number */ 8 __u16 csize; /* Attached crypto information size */ 9 __u16 cpad; /* Attached padding size */ 10 __u16 ext; /* External flags */ 11 __u32 size; /* Size of the attached data */ 12 __u32 trans; /* Transaction id */ 13 __u64 id; /* Object ID to operate on. Used for feedback.*/ 14 __u64 start; /* Start of the object. */ 15 __u64 iv; /* IV sequence */ 16 __u8 data[0]; 17 }; 18 19 Commands can be embedded into transaction command (which in turn has own command), 20 so one can extend protocol as needed without breaking backward compatibility as long 21 as old commands are supported. All string lengths include tail 0 byte. 22 23 All commands are transferred over the network in big-endian. CPU endianness is used at the end peers. 24 25 @cmd - command number, which specifies command to be processed. Following 26 commands are used currently: 27 28 NETFS_READDIR = 1, /* Read directory for given inode number */ 29 NETFS_READ_PAGE, /* Read data page from the server */ 30 NETFS_WRITE_PAGE, /* Write data page to the server */ 31 NETFS_CREATE, /* Create directory entry */ 32 NETFS_REMOVE, /* Remove directory entry */ 33 NETFS_LOOKUP, /* Lookup single object */ 34 NETFS_LINK, /* Create a link */ 35 NETFS_TRANS, /* Transaction */ 36 NETFS_OPEN, /* Open intent */ 37 NETFS_INODE_INFO, /* Metadata cache coherency synchronization message */ 38 NETFS_PAGE_CACHE, /* Page cache invalidation message */ 39 NETFS_READ_PAGES, /* Read multiple contiguous pages in one go */ 40 NETFS_RENAME, /* Rename object */ 41 NETFS_CAPABILITIES, /* Capabilities of the client, for example supported crypto */ 42 NETFS_LOCK, /* Distributed lock message */ 43 NETFS_XATTR_SET, /* Set extended attribute */ 44 NETFS_XATTR_GET, /* Get extended attribute */ 45 46 @ext - external flags. Used by different commands to specify some extra arguments 47 like partial size of the embedded objects or creation flags. 48 49 @size - size of the attached data. For NETFS_READ_PAGE and NETFS_READ_PAGES no data is attached, 50 but size of the requested data is incorporated here. It does not include size of the command 51 header (struct netfs_cmd) itself. 52 53 @id - id of the object this command operates on. Each command can use it for own purpose. 54 55 @start - start of the object this command operates on. Each command can use it for own purpose. 56 57 @csize, @cpad - size and padding size of the (attached if needed) crypto information. 58 59 Command specifications. 60 61 @NETFS_READDIR 62 This command is used to sync content of the remote dir to the client. 63 64 @ext - length of the path to object. 65 @size - the same. 66 @id - local inode number of the directory to read. 67 @start - zero. 68 69 70 @NETFS_READ_PAGE 71 This command is used to read data from remote server. 72 Data size does not exceed local page cache size. 73 74 @id - inode number. 75 @start - first byte offset. 76 @size - number of bytes to read plus length of the path to object. 77 @ext - object path length. 78 79 80 @NETFS_CREATE 81 Used to create object. 82 It does not require that all directories on top of the object were 83 already created, it will create them automatically. Each object has 84 associated @netfs_path_entry data structure, which contains creation 85 mode (permissions and type) and length of the name as long as name itself. 86 87 @start - 0 88 @size - size of the all data structures needed to create a path 89 @id - local inode number 90 @ext - 0 91 92 93 @NETFS_REMOVE 94 Used to remove object. 95 96 @ext - length of the path to object. 97 @size - the same. 98 @id - local inode number. 99 @start - zero. 100 101 102 @NETFS_LOOKUP 103 Lookup information about object on server. 104 105 @ext - length of the path to object. 106 @size - the same. 107 @id - local inode number of the directory to look object in. 108 @start - local inode number of the object to look at. 109 110 111 @NETFS_LINK 112 Create hard of symlink. 113 Command is sent as "object_path|target_path". 114 115 @size - size of the above string. 116 @id - parent local inode number. 117 @start - 1 for symlink, 0 for hardlink. 118 @ext - size of the "object_path" above. 119 120 121 @NETFS_TRANS 122 Transaction header. 123 124 @size - incorporates all embedded command sizes including theirs header sizes. 125 @start - transaction generation number - unique id used to find transaction. 126 @ext - transaction flags. Unused at the moment. 127 @id - 0. 128 129 130 @NETFS_OPEN 131 Open intent for given transaction. 132 133 @id - local inode number. 134 @start - 0. 135 @size - path length to the object. 136 @ext - open flags (O_RDWR and so on). 137 138 139 @NETFS_INODE_INFO 140 Metadata update command. 141 It is sent to servers when attributes of the object are changed and received 142 when data or metadata were updated. It operates with the following structure: 143 144 struct netfs_inode_info 145 { 146 unsigned int mode; 147 unsigned int nlink; 148 unsigned int uid; 149 unsigned int gid; 150 unsigned int blocksize; 151 unsigned int padding; 152 __u64 ino; 153 __u64 blocks; 154 __u64 rdev; 155 __u64 size; 156 __u64 version; 157 }; 158 159 It effectively mirrors stat(2) returned data. 160 161 162 @ext - path length to the object. 163 @size - the same plus size of the netfs_inode_info structure. 164 @id - local inode number. 165 @start - 0. 166 167 168 @NETFS_PAGE_CACHE 169 Command is only received by clients. It contains information about 170 page to be marked as not up-to-date. 171 172 @id - client's inode number. 173 @start - last byte of the page to be invalidated. If it is not equal to 174 current inode size, it will be vmtruncated(). 175 @size - 0 176 @ext - 0 177 178 179 @NETFS_READ_PAGES 180 Used to read multiple contiguous pages in one go. 181 182 @start - first byte of the contiguous region to read. 183 @size - contains of two fields: lower 8 bits are used to represent page cache shift 184 used by client, another 3 bytes are used to get number of pages. 185 @id - local inode number. 186 @ext - path length to the object. 187 188 189 @NETFS_RENAME 190 Used to rename object. 191 Attached data is formed into following string: "old_path|new_path". 192 193 @id - local inode number. 194 @start - parent inode number. 195 @size - length of the above string. 196 @ext - length of the old path part. 197 198 199 @NETFS_CAPABILITIES 200 Used to exchange crypto capabilities with server. 201 If crypto capabilities are not supported by server, then client will disable it 202 or fail (if 'crypto_fail_unsupported' mount options was specified). 203 204 @id - superblock index. Used to specify crypto information for group of servers. 205 @size - size of the attached capabilities structure. 206 @start - 0. 207 @size - 0. 208 @scsize - 0. 209 210 @NETFS_LOCK 211 Used to send lock request/release messages. Although it sends byte range request 212 and is capable of flushing pages based on that, it is not used, since all Linux 213 filesystems lock the whole inode. 214 215 @id - lock generation number. 216 @start - start of the locked range. 217 @size - size of the locked range. 218 @ext - lock type: read/write. Not used actually. 15'th bit is used to determine, 219 if it is lock request (1) or release (0). 220 221 @NETFS_XATTR_SET 222 @NETFS_XATTR_GET 223 Used to set/get extended attributes for given inode. 224 @id - attribute generation number or xattr setting type 225 @start - size of the attribute (request or attached) 226 @size - name length, path len and data size for given attribute 227 @ext - path length for given object