Pfs_types

/* $Id: pfs_types.x 235 2010-06-20 22:23:05Z gerd $ -*- c -*- */

Types for the RPC interfaces

For users of the Plasma_client module: The types defined here are mapped to corresponding Ocaml types, and exported via the Plasma_rpcapi_aux module.

Within the server, however, the mappings of Pfs_rpcapi_aux are used. (These mappings differ in some minor points from the ones used for the client.)

#ifndef PFS_TYPES_X
#define PFS_TYPES_X

longstring

typedef string longstring<>;

A string up to 4G length

longstrings

typedef longstring longstrings<>;

An array of longstrings

longstring_opt

typedef longstring *longstring_opt;

A longstring option

hypers

typedef hyper hypers<>;

An array of hypers

trans_id

typedef hyper trans_id;

transaction IDs can be used to run several transactions over the same TCP connection

ug

struct ug {
    longstring user;
    longstring group;
};

Users and groups are given by name

time

struct time {
    hyper tsecs;  /* Seconds since the epoch... */
    int   tnsecs; /* plus these nanoseconds */
};

tsecs and tnsecs must be non-negative; tnsecs < 1E9. In the filesystem procedure update_inodeinfo a negative tsecs is interpreted as "set the time to the current server time"

time_opt

typedef time *time_opt;

an optional time struct

ftype_enum

enum ftype_enum {
    FTYPE_REGULAR = 0,
    FTYPE_DIRECTORY = 1,
    FTYPE_SYMLINK = 2
};

File types

ftype

union ftype switch(ftype_enum d) {
  case FTYPE_REGULAR: 
    void;
  default:
    void;
};

File types as union

blockinfo

blockinfo says where the n-th block of a file is stored on a datanode. The number n is called the block index (starting at 0). The datanode location is given by the identity of the datanode, and the block number of the datanode. Block numbers count from 0 to s-1 when s is the number of blocks a datanode stores.

In blockinfo there is also the information to which machine the identity of the datanode is assigned, and whether the machine is alive. This is purely informational, and is intended to ease the implementation of clients.

Checksums are not yet implemented.

The sequence number of the inode is increased whenever new data is written. It is also included in blockinfo to simplify the implementation of caches.

Safe transactions: The numbers safetrans_id and safetrans_vfy need to be passed on to the datanode in order to read or write the block. The numbers are only valid for the current transaction, and only for this block. The numbers form together a ticket that allows accesses to the block. (Actually, the datanode only checks for writes whether the client has a valid ticket, but not for reads. This might change in the future, though.)

struct blockinfo {
    hyper      index;         /* block index */
    longstring node;          /* datanode server as "host:port" ("" if not known) */
    longstring identity;      /* datanode server as identity string */
    hyper      block;         /* block number on this node */
    bool       node_alive;    /* informational: whether the node is alive */
    longstring *checksum;     /* optional checksum */
    hyper      inode_seqno;   /* current seqno of the inode */
    hyper      safetrans_id;  /* safetrans ticket, first part */
    hyper      safetrans_tmo; /* safetrans ticket, timeout */
    hyper      safetrans_vfy; /* safetrans ticket, second part */
};

Safe transactions

safetrans_*: For securing the communication with the datanode. The blocks are accessible for a limited period of time only. The safetrans_id identifies the datanode transaction. safetrans_tmo is the point in time when the access times out. After that the data nodes will not accept writes to the blocks any longer. The verifier safetrans_vfy is a hash value built from the safetrans_id and the block number, and is used by the data node to check that only accessible blocks are written:

safetrans_vfy=extract_64_bits(MD5(safetrans_id ^ "/" ^ 
        safetrans_secret ^ "/" ^ block))

Usually, the safetrans feature is only used for securing block writes. The protocol would also allow it to use it for reads, though, and compatible clients should assume this.

blocklist

Block lists describe where the blocks of a file are stored. Note that these phenomenons can occur:

• the same block index can occur several times (replicas)
• a certain block index does not occur at all (a file hole)
• all blockinfo structs for a block index say that the datanode is down (a broken file)

typedef blockinfo blocklist<>;

inodeinfo

inodeinfo is what is stored for an inode. Documentation is inline below. Note that inodeinfo structs may be passed from the server to the client, and from the client to the server. In the latter case, the client may not know all fields, or may use special values in fields.

struct inodeinfo {
    ftype filetype;

• The file type. Some fields are only meaningful for certain types.

    ug    usergroup;

• The owner

    int   mode;

• File permission bits

    hyper eof;

• The eof value is seen as a convention only. The server never automatically changes it when blocks are allocated or freed. This means eof can be set to a position before the last block or after the last block. It is just the interpretation of the user to use this number as eof position.

  Conventionally, eof is only meaningful for regular files.

    time  mtime;
    time  ctime;

• Time fields are not automatically maintained, except that a link or unlink operation implicitly updates the mtime of the directory. See the documentation for time how clients can request that the server fills in its own current time.

    int   replication;   

• The replication factor the file ought to have. Clients can set it to 0 to request the default replication factor. Values returned from the server are always >= 1.

  Replication is only meaningful for regular files.

    hyper blocklimit;

• The blocks from the index blocklimit on are not allocated. This field cannot be set by clients - the field value is ignored.

  Note that this is totally unrelated to eof which can be set to any value independent on how many blocks are allocated.

  Also, there may be holes in the file before blocklimit.

    
    longstring field1;

• For symlinks this is the target. For other types this field has no defined meaning

    hyper seqno;

• This is increased by the server whenever blocks are allocated or freed, i.e for every content modification of the file. It is not possible to change this field. This means one can easily check for any file modification by comparing the inodeinfo fields which are guaranteed to change for every data or metadata modification.

    hyper create_verifier;

• intended use as NFSv3 create verifier. Set to 0 outside NFS scope.

};

entry

Entries of directories

struct entry {
    longstring entry_name;    /* basename of a file in a directory */
    hyper      entry_inode;   /* inode of this file */
};

entries

typedef entry entries<>;

fsstat

struct fsstat {
    hyper    total_blocks;
    hyper    used_blocks;
    hyper    trans_blocks;

• Blocks in a transitional phase: these are allocated by a transaction, but the transaction is not yet committed

    bool     have_block_checksums;

• Whether this feature is enabled

    bool     have_safetrans_for_reads;

• whether safetrans ID's are required for read access

    bool     have_protected_inodes;

• whether Filesystem users may only pass inode numbers to RPC's that have been returned by previously called RPC's in the same transaction

};

errno_code

enum errno_code {
    OK = 0,
    ENOTRANS = 1,         /* no transaction */
    EFAILEDCOMMIT = 2,    /* general commit error */
    ELONGTRANS = 3,       /* transaction too long */
    EFAILED = 4,          /* general error */
    EPERM = 5,            /* not owner, or op is otherwise not permitted */
    ENOENT = 6,           /* No such file or directory */
    EACCESS = 7,          /* Permission denied */
    EEXIST = 8,           /* File exists */
    EFHIER = 9,           /* File hierarchy violation */
    EINVAL = 10,          /* invalid argument */
    EFBIG = 11,           /* file too big */
    ENOSPC = 12,          /* no space left */
    EROFS = 13,           /* read-only filesystem */
    ENAMETOOLONG = 14,    /* filename too long */
    ECONFLICT = 15,       /* update conflicts with another transaction */
    ECOORD = 16,          /* this is not the coordinator */
    ENONODE = 17,         /* unknown node */
    ETBUSY = 18,          /* transaction is busy (last command not finished) */
    ENOIENT = 19,         /* no such inode */
    EIO = 20              /* datanode error, not enough datanodes */
};

Result types of RPC's

This macro is used for creating the result types of Filesystem RPC's. These results are always unions of the possible error codes with the special value OK. For OK, a value of some type is returned as result value, and this type is the second parameter.

#define MK_RESULT_TYPE(name,type)        \
  union name switch(errno_code d) {      \
    case OK:                             \
      type;                              \
    default:                             \
      void;                              \
  }

Creates the types:

• rvoid
• rinodeinfo
• rblocklist
• rfsstat
• rint
• rhyper
• rhypers
• rlongstrings
• rentries

MK_RESULT_TYPE(rvoid,void);
MK_RESULT_TYPE(rinodeinfo,inodeinfo t);
MK_RESULT_TYPE(rblocklist,blocklist t);
MK_RESULT_TYPE(rfsstat,fsstat t);
MK_RESULT_TYPE(rint,int t);
MK_RESULT_TYPE(rhyper,hyper t);
MK_RESULT_TYPE(rhypers,hypers t);
MK_RESULT_TYPE(rlongstrings,longstrings t);
MK_RESULT_TYPE(rentries,entries t);



/* Revision numbers have the format:

   YYYYMMDDHHMMSSUUUUUU:<random hex digits>

   It is meaningful to sort revision numbers.
*/

#ifdef SERVER_CONTEXT

readdata in server context

typedef string readdata<>;

writedata in server context

typedef _managed string writedata<>;

(A managed string is represented differently in Ocamlnet's language mapping layer.)

announcement in server context

struct announcement {
    longstring     ann_clustername;
    /* clustername */

    longstring     ann_sender;
    /* sender host:port */

    longstrings    ann_eligible;
    /* list of hosts that are eligible (host:port syntax) */

    longstring     ann_revision;
    /* the revision number of the sender */

    longstring     ann_rank;
    /* configured rank */
};

#else

readdata in client context

typedef _managed string readdata<>;

writedata in client context

typedef _managed string writedata<>;

#endif

dn_channel_enum

Block data can be exchanged with the datanode servers on two ways:

1. The block data is included in the normal RPC call as string
2. The block data is put into a shared memory object

Of course, the second method works only if the client and the server are on the same node. Also, the client needs to invoke the server RPC via a Unix Domain socket, and not via TCP.

More methods may be defined in the future.

enum dn_channel_enum {
    DNCH_RPC = 0,   /* the data is embedded into the RPC channel */
    DNCH_SHM = 1    /* the data is exchanged via a POSIX shm object */
};

dn_channel_shm_obj

This struct identifies a shared memory object

struct dn_channel_shm_obj {
    longstring shm_path;     /* must be a path for POSIX shm */
    hyper      shm_offset;   /* the offset to the start in the file. */
    int        shm_length;   /* the length of the object */
};

dn_channel_rd_req

This is the argument for data reads. The client can request the data exchange method. For shared memory, the client also has to say which shared memory object will receive the data.

union dn_channel_rd_req switch (dn_channel_enum d) {
case DNCH_RPC:
    void;
case DNCH_SHM:
    dn_channel_shm_obj ch;
};

dn_channel_rd_data

This is the return value of the data server for a read request. If the data is included in the RPC message, it follows now. If the data is put into shared memory, the client can now expect it to be there.

union dn_channel_rd_data switch (dn_channel_enum d) {
case DNCH_RPC:
    readdata data;
case DNCH_SHM:
    void;
};

dn_channel_wr_data

For write requests, the client either includes the data directly in the message, or it has already put it into a shared memory objects, and only includes the information where

union dn_channel_wr_data switch (dn_channel_enum d) {
case DNCH_RPC:
    writedata data;
case DNCH_SHM:
    dn_channel_shm_obj ch;
};
#endif

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