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Module Plasma_client

module Plasma_client: sig .. end
Client access to the Plasma Filesystem

This is a client library providing full access to the Plasma filesystem. It is probably intuitive to understand this interface, but if any question pops up, please consult the page Plasmafs_protocol. It explains all background concepts of the PlasmaFS protocol.


Many of the following functions return so-called engines. These functions have the suffix _e. There is always a "normal", i.e. synchronous variant not returning engines computing the result, but directly the result. The engines make it possible to send queries asynchronously. For more information about engines, see the module Uq_engines of Ocamlnet. It is generally not possible to use the client in a synchronous way when an engine is still running.

Opening PlasmaFS

How do you open the PlasmaFS filesystem? This depends. If you are writing a map/reduce program, the simplest way is:

      let esys = Unixqueue.create_unix_event_system() 
      let cluster =
	match me # filesystem # open_cluster "plasma::/" esys with
	 | None -> failwith "No access to PlasmaFS"
	 | Some c -> c

Then cluster is a Plasma_client.plasma_cluster that is already minimally configured. You will run into the "failwith" case when PlasmaFS is disabled in the configuration file of the map/reduce job. The object me is the Mapred_def.mapred_env environment coming from the main program.

If you are writing an independent application, the recommended way is:

       let cluster = ref None
       let namenodes = ref []
       let () =
           [ "-cluster", Arg.String (fun s -> cluster := Some s),
             "<name>    Set the cluster name";
             "-namenode", Arg.String (fun n -> namenodes := n :: !namenodes),
             "<host>:<port>   Also use this namenode";

       let cluster_config =
          ?nn_nodes:(if !namenodes=[] then None else Some !namenodes)
       let esys = Unixqueue.create_unix_event_system() 
       let cluster =
         Plasma_client.open_cluster_cc cluster_config esys 
       Plasma_client.configure_auth_daemon cluster

This results in the conventional behavior:

  • The options -cluster and -namenode can be used to override defaults
  • The defaults are taken from the file ~/.plasmafs
  • Authentication is done via the authentication daemon

Some of the following types are defined in Plasma_rpcapi_aux, especially
  • Plasma_rpcapi_aux.inodeinfo
  • Plasma_rpcapi_aux.fsstat
  • Plasma_rpcapi_aux.blockinfo

type plasma_cluster 
an open Plasma cluster
type plasma_trans 
plasma transaction
type inode = int64 
inodes are int64 numbers
type errno = [ `eaccess
| `ebadpath
| `econflict
| `ecoord
| `eexist
| `efailed
| `efailedcommit
| `efbig
| `efhier
| `einval
| `eio
| `eisdir
| `elongtrans
| `eloop
| `enametoolong
| `enoent
| `enonode
| `enospc
| `enotdir
| `enotempty
| `enotrans
| `eperm
| `erofs
| `estale
| `etbusy ]
see errno_code for documentation
type topology = [ `Chain | `Star ] 
see copy_in
type copy_in_flags = [ `Late_datasync | `No_datasync | `Retry ] 
see copy_in
type copy_out_flags = [ `No_truncate | `Retry ] 
see copy_out
exception Plasma_error of errno
Error reported by the server
exception Cluster_down of string
No access to the cluster possible
exception Datanode_error of exn
The exception was thrown while accessing a data node

Open cluster

val open_cluster : string ->
(string * int) list -> Unixqueue.event_system -> plasma_cluster
open_cluster name namenodes: Opens the cluster with these namenodes (given as (hostname,port) pairs). The client automatically determines which is the coordinator.
val open_cluster_cc : Plasma_client_config.client_config ->
Unixqueue.event_system -> plasma_cluster
Same, but takes a Plasma_client_config.client_config object which can in turn be obtained via Plasma_client_config.get_config.
val open_cluster_like : ?same_buffer:bool ->
?same_pref_nodes:bool ->
?same_shm_manager:bool ->
plasma_cluster ->
Unixqueue.event_system -> plasma_cluster
Opens a cluster with a configuration taken from an existing cluster. The cluster name, the namenode configuration, and the type of authentication is always taken over. The rest can be configured with the same_* flags.
val event_system : plasma_cluster -> Unixqueue.event_system
Returns the event system
val sync : ('a -> 'b Uq_engines.engine) -> 'a -> 'b
Waits until the event system is done and returns the result of the engine
val dump_buffers : plasma_cluster -> unit
debug report
val close_cluster : plasma_cluster -> unit
Closes all file descriptors permanently
val abort_cluster : plasma_cluster -> unit
Closes the descriptors to remote services so far possible, but does not permanently shut down the client functionality. The descriptors are automatically opened again when needed. The effect is not only that resources are given back temporarily, but also that the pending transactions are aborted.
val cluster_name : plasma_cluster -> string
Returns the cluster name
val cluster_namenodes : plasma_cluster -> (string * int) list
Returns the namenodes passed to open_cluster
val configure_buffer : plasma_cluster -> int -> unit
configure_buffer c n: configures to use n buffers. Each buffer is one block. These buffers are only used for buffered I/O, i.e. for and Plasma_client.write, but not for Plasma_client.copy_in and Plasma_client.copy_out.
val configure_pref_nodes : plasma_cluster -> string list -> unit
Configures that the data nodes with the given identities are preferred for the allocation of new blocks. This config is active until changed again. Useful for configuring local identities (see local_identities below), i.e. for enforcing that blocks are allocated on the same machine, so far possible.
val configure_pref_nodes_of_inode : plasma_cluster -> int64 -> string list option -> unit
Similar to configure_pref_nodes, but this list overrides the global setting for this inode.
val configure_shm_manager : plasma_cluster -> Plasma_shm.shm_manager -> unit
Configures a shared memory manager. This is an optional feature. The manager must be configured before the cluster is used.
val shm_manager : plasma_cluster -> Plasma_shm.shm_manager
Returns the current manager
val blocksize_e : plasma_cluster -> int Uq_engines.engine
val blocksize : plasma_cluster -> int
Returns the blocksize
val params_e : plasma_cluster -> (string * string) list Uq_engines.engine
val params : plasma_cluster -> (string * string) list
Returns a list of client parameters
val fsstat_e : plasma_cluster -> Plasma_rpcapi_aux.fsstat Uq_engines.engine
val fsstat : plasma_cluster -> Plasma_rpcapi_aux.fsstat
Return statistics
val local_identities_e : plasma_cluster -> string list Uq_engines.engine
val local_identities : plasma_cluster -> string list
Return the identities of the data nodes running on this machine (for configure_pref_nodes)
val get_dn_info_e : plasma_cluster ->
Plasma_rpcapi_aux.dn_info array Uq_engines.engine
val get_dn_info : plasma_cluster -> Plasma_rpcapi_aux.dn_info array
Return information about all enabled and live datanodes (includes identity, size, and host)

Authentication and impersonation

There is a distinction between authentication on the RPC level, and authentication on the filesystem level. For RPC, the client has only the choice between two user IDs, namely "proot" and "pnobody". The first has all rights, whereas the latter one can only connect (unless it tries to get more rights). Non-privileged clients use "pnobody" and provide an additional authentication ticket to obtain additional permissions.

On the filesystem level, the client can take over any user ID independent of what ID was used on the RPC level. If "proot" is the RPC user, one can just become any filesystem user without credentials. If "pnobody" is the RPC user, one needs an authentication ticket to become a certain user on the filesystem level.

There are two ways of getting a ticket:

  • By calling Plasma_client.get_auth_ticket in a session one can obtain a ticket, and use it in further sessions to become again the same user (via Plasma_client.impersonate).
  • By contacting the authentication daemon, one can get a ticket for the Unix-level user ID. (Only on system where this daemon is locally runnig.)

val configure_auth : plasma_cluster ->
string -> string -> (string -> string) -> unit
configure_auth c nn_user dn_user get_password: Configures that accesses to the namenode are authenticated on the RPC level as nn_user and accesses to datanodes are authenticated as dn_user. The function get_password is called to obtain the password for a user.

nn_user can be set to "proot" or "pnobody".

dn_user is normally set to "pnobody".

This type of authentication does not imply any impersonation on the filesystem level. One should run Plasma_client.impersonate to set something.

val configure_auth_daemon : plasma_cluster -> unit
Configures that the authentication daemon is contacted to get evidence about the current user. If this fails, the namenode is contacted anonymously (which normally will also fail).

This mode also impersonates on the filesystem level.

val configure_auth_ticket : plasma_cluster -> string -> unit
Configures that this ticket proves the identity of the user.

This mode also impersonates on the filesystem level.

val impersonate_e : plasma_cluster ->
string -> string -> string list -> string option -> unit Uq_engines.engine
val impersonate : plasma_cluster ->
string -> string -> string list -> string option -> unit
impersonate c user group supp_groups ticket: Become the user on the filesystem level. The main group is group, and the supplementary groups are supp_groups.

The ticket is necessary when the new privileges are not implied by the existing privileges (i.e one can only give up rights when a ticket is lacking). Examples when a ticket is not required:

  • The user on the RPC level is "proot": existing superuser privileges can be given up with impersonate.
  • The user does not change, but only the main group is set to a different member of the supplementary groups.
A ticket can be obtained with Plasma_client.get_auth_ticket.

impersonate must not be used inside transactions.

val get_auth_ticket_e : plasma_cluster -> string -> string Uq_engines.engine
val get_auth_ticket : plasma_cluster -> string -> string
get_auth_ticket user: Get an authentication ticket for this user
val current_user_e : plasma_cluster ->
(string * string * string list) Uq_engines.engine
val current_user : plasma_cluster -> string * string * string list
let (user,group,supp_groups) = current_user c: Get the identity of the current client principal on the filesystem level.

Indicates `efailed if no impersonation has been done yet.

val configure_default_user_group : plasma_cluster -> string -> string -> unit
configure_default_user_group c user group: Normally, new files are created as the user and group corresponding to the current impersonation. If privileges permit it, this can changed here so that files are created as user and group. Each string can be empty, in which case the value is taken from the impersonation.

This is especially useful if one authenticates as "proot" and does not do any impersonation, i.e. the superuser privileges are still in effect. Another use is to create files with a group that is different from the main group of the current impersonation.

This affects not only files, but also new directories and symlinks.


All functions requiring a plasma_trans value as argument must be run inside a transaction. This means one has to first call start to open the transaction, call then the functions covered by the transaction, and then either commit or abort.

It is allowed to open several transactions simultaneously.

If you use the engine-based interface, it is important to ensure that the next function in a transaction can first be called when the current function has responded the result. This restriction is only valid in the same transaction - other transactions are totally independent in this respect.

val start_e : plasma_cluster -> plasma_trans Uq_engines.engine
val start : plasma_cluster -> plasma_trans
Starts a transaction
val commit_e : plasma_trans -> unit Uq_engines.engine
val commit : plasma_trans -> unit
Commits a transaction, and makes the changes of the transaction permanent.
val abort_e : plasma_trans -> unit Uq_engines.engine
val abort : plasma_trans -> unit
Aborts a transaction, and abandons the changes of the transaction
val cluster : plasma_trans -> plasma_cluster
the cluster to which a transaction belongs

File creation/access over the inode interface

val create_inode_e : plasma_trans ->
Plasma_rpcapi_aux.inodeinfo -> inode Uq_engines.engine
val create_inode : plasma_trans ->
Plasma_rpcapi_aux.inodeinfo -> inode
Create a new inode. The inode does initially not have a name.

At the end of the transaction inodes are automatically deleted that do not have a name. Use link_e to assign names (below).

See also Plasma_client.create_file below, which immediately links the inode to a name. See also Plasma_client.regular_ii, Plasma_client.dir_ii, and Plasma_client.symlink_ii for how to create inodeinfo values.

val delete_inode_e : plasma_trans -> inode -> unit Uq_engines.engine
val delete_inode : plasma_trans -> inode -> unit
Delete the inode
val get_inodeinfo_e : plasma_trans ->
inode -> Plasma_rpcapi_aux.inodeinfo Uq_engines.engine
val get_inodeinfo : plasma_trans ->
inode -> Plasma_rpcapi_aux.inodeinfo
Get info about inode. This returns the inodeinfo record from the perspective of this transaction.
val get_cached_inodeinfo_e : plasma_cluster ->
inode -> bool -> Plasma_rpcapi_aux.inodeinfo Uq_engines.engine
val get_cached_inodeinfo : plasma_cluster ->
inode -> bool -> Plasma_rpcapi_aux.inodeinfo
Get info about inode. This function returns the inodeinfo record from the cache. The cache can only contain committed versions of the inodeinfo record, and it is tried that only recent versions are in the cache. If the cache does not contain the data, or if the data is out of date, a new transaction is started to get the newest committed version.

The bool argument can be set to true to enforce that the newest version is retrieved. However, there is no guarantee that the returned version is still the newest one when this function returns.

Note that get_inodeinfo also implicitly refreshes the cache when the transaction is (still) only used for read accesses.

The returned inodeinfo does not include modifications caused by block writes that were not yet flushed to disk.

val set_inodeinfo_e : plasma_trans ->
inode -> Plasma_rpcapi_aux.inodeinfo -> unit Uq_engines.engine
val set_inodeinfo : plasma_trans ->
inode -> Plasma_rpcapi_aux.inodeinfo -> unit
set info about inode. Note that setting EOF does neither increase nor reduce the number of allocated blocks.
val truncate_e : plasma_trans ->
inode -> int64 -> unit Uq_engines.engine
val truncate : plasma_trans -> inode -> int64 -> unit
Sets EOF value, and all blocks beyond EOF are deallocated.

Fast sequential data access

The function copy_in writes a local file to the cluster. copy_out reads a file from the cluster and copies it into a local file.

Especially copy_in works only in units of whole blocks. The function never reads a block from the filesystem, modifies it, and writes it back. Instead, it writes the block with the data it has, and if there is still space to fill, it pads the block with zero bytes. If you need support for updating parts of a block only, better use the buffered access below.

val copy_in_e : ?flags:copy_in_flags list ->
plasma_cluster ->
inode ->
int64 ->
Unix.file_descr -> int64 -> topology -> int64 Uq_engines.engine
val copy_in : ?flags:copy_in_flags list ->
plasma_cluster ->
inode ->
int64 -> Unix.file_descr -> int64 -> topology -> int64
copy_in_e c inode pos fd len: Copies the data from the file descriptor fd to the file given by inode. The data is taken from the current position of the descriptor. Up to len bytes are copied. The data is written to position pos of the file referenced by the inode. If it is written past the EOF position of the destination file, the EOF position is advanced. The function returns the number of copied bytes.

For seekable descriptors, len specifies the exact number of bytes to copy. If the input file is shorter, null bytes are appended to the file until len is reached.

For non-seekable descriptors, an additional buffer needs to be allocated. Also, len is ignored for non-seekable descriptors - data is always copied until EOF is seen. (However, in the future this might be changed. It is better to pass Int64.max_int as len if unlimited copying is required.)

topology says how to transfer data from the client to the data nodes. `Star means the client organizes the writes to the data nodes as independent streams. `Chain means that the data is first written to one of the data nodes, and the replicas are transferred from there to the next data node.


  • `No_datasync: Data blocks are not synchronized to disk
  • `Late_datasync: Only the last block is synchronized to disk. This also includes are preceding blocks. If an error occurs, though, nothing is guaranteed.
  • `Retry: For qualifying errors, the inner transactions are repeated until successful, or the timeout is exceeded. This includes ECONFLICT and EIO.
The default is to write synchronously: At the end of each transaction copy_in commits, all blocks are guaranteed to be on disk.

Limitation: pos must be a multiple of the blocksize. The file is written in units of the blocksize (i.e. blocks are never partially updated).

copy_in performs its operations always in separate transactions.

val copy_in_from_buf_e : ?flags:copy_in_flags list ->
plasma_cluster ->
inode ->
int64 ->
Netsys_mem.memory -> int -> topology -> int Uq_engines.engine
val copy_in_from_buf : ?flags:copy_in_flags list ->
plasma_cluster ->
inode ->
int64 -> Netsys_mem.memory -> int -> topology -> int
copy_in_from_buf c inode pos buf len: Copies the data from buf to the file denoted by inode. The data is taken from the beginning of buf, and the length is given by len. The data is written to position pos of inode.

copy_in_from_buf works much in the same way as copy_in, only that the data is taken from a buffer and not from a file descriptor.

val copy_out_e : ?flags:copy_out_flags list ->
plasma_cluster ->
inode ->
int64 -> Unix.file_descr -> int64 -> int64 Uq_engines.engine
val copy_out : ?flags:copy_out_flags list ->
plasma_cluster ->
inode -> int64 -> Unix.file_descr -> int64 -> int64
copy_out_e c inode pos fd len Copies the data from the file referenced by inode to file descriptor fd. The data is taken from position pos to pos+len-1 of the file, and it is written to the current position of fd. The number of copied bytes is returned.

Seekable output files may only be extended, but are never truncated.

For non-seekable descriptors, an additional buffer needs to be allocated.

If there are holes in the input file, the corresponding byte region is filled with zero bytes in the output. If it is tried to read past EOF, this is not prevented, but handled as if the region past EOF was a file hole.

Limitation: pos must be a multiple of the blocksize.

copy_out performs its operations always in separate transactions.


  • `No_truncate: The descriptor fd is not truncated to the real file size
  • `Retry: For qualifying errors, the inner transactions are repeated until successful, or the timeout is exceeded. This includes ECONFLICT and EIO.

val copy_out_to_buf_e : ?flags:copy_out_flags list ->
plasma_cluster ->
inode ->
int64 -> Netsys_mem.memory -> int -> int Uq_engines.engine
val copy_out_to_buf : ?flags:copy_out_flags list ->
plasma_cluster ->
inode -> int64 -> Netsys_mem.memory -> int -> int
copy_out_to_buf_e c inode pos buf len Copies the data from the file denoted by inode to the buffer buf. The data is taken from position pos to pos+len-1 of the file, and it is written to the beginning of buf.

Buffered data access

The functions in this section use a (potentially) big internal buffer that exists within Plasma_client.plasma_cluster. This buffer contains file blocks that have already been read, and serves as a cache for future reads. Also, it buffers modifications of file blocks ("dirty blocks"), and when the buffer is full or flushed, the modifications are written to PlasmaFS in one go.

This works similar to a normal file buffer with one difference: The buffer is shared by all files.

For getting well-performing buffered access, you should configure the size of the buffer via Plasma_client.configure_buffer. It defaults to a very small value.

Note that the buffer is completely ignored by the above copy_in_* and copy_out_* functions.

type strmem = [ `Memory of Netsys_mem.memory | `String of string ] 
The user buffer for read and write can be given as string or as bigarray (memory). The latter is advantageous, because there are some optimizations that are only applicable to bigarrays.
val read_e : ?lazy_validation:bool ->
plasma_cluster ->
inode ->
int64 ->
strmem ->
int -> int -> (int * bool * Plasma_rpcapi_aux.inodeinfo) Uq_engines.engine
val read : ?lazy_validation:bool ->
plasma_cluster ->
inode ->
int64 ->
strmem ->
int -> int -> int * bool * Plasma_rpcapi_aux.inodeinfo
read_e c inode pos s spos len: Reads data from inode, and returns (n,eof,ii) where n is the number of read bytes, and eof the indicator that EOF was reached. This number n may be less than len only if EOF is reached. ii is the current inodeinfo.

Before a read is responded from a clean buffer it is checked whether the buffer is still up to date.

By default, read fetches the metadata from the namenode before starting any transaction. By setting lazy_validation, one can demand a different mode, where these fetches can be delayed by a short period of time (useful when several reads are done in sequence for the same file; only the first read sets ~lazy_validation:false, and the remaining ones ~lazy_validation:true).

type read_request = int64 * strmem * int * int 
type read_response = int * bool * Plasma_rpcapi_aux.inodeinfo 
type multi_read_task = (read_request * (read_response -> unit)) option
val multi_read_e : ?lazy_validation:bool ->
plasma_cluster ->
inode ->
multi_read_task Stream.t -> unit Uq_engines.engine
multi_read_e c inode stream: This version of read allows it to read multiple times from the same file. All reads are done in the same transaction.

The function gets the next task from stream when the previous task is done (if any). A task is always an engine which results either in None (ending the stream), or in Some(req,pass_resp). The request req = (pos, s, spos, len) says from where to take the data and where to store it (like in read_e). The response resp = (n,eof,ii) is the argument of pass_resp.

val write_e : plasma_cluster ->
inode ->
int64 -> strmem -> int -> int -> int Uq_engines.engine
val write : plasma_cluster ->
inode -> int64 -> strmem -> int -> int -> int
write_e c inode pos s spos len: Writes data to inode and returns the number of written bytes. This number n may be less than len for arbitrary reasons (unlike read - to be fixed).

A write that is not aligned to a block implies that the old version of the block is read first (if not available in a buffer). This is a big performance penalty, and best avoided.

It is not ensured that the write is completed when the return value becomes available. The write is actually done in the background, and can be explicitly triggered with the flush_e operation. Also, note that the write happens in a separate transaction. (With "background" we do not mean a separate kernel thread, but an execution thread modeled with engines.)

Writing also triggers that the EOF position is at least set to the position after the last written position. However, this is first done when the blocks are flushed in the background. (Use get_write_eof to get this value immediately, before flushing.)

As writing happens in the background, some special attention has to be paid for the way errors are reported. At the first error the write thread stops, and an error code is set. This code is reported at the next write or flush. After being reported, the code is cleared again. Writing is not automatically resumed - only further write and flush invocations will restart the writing thread. Also, the data buffers are kept intact after errors - so everything will be again tried to be written (which may run into the same error). The function drop_inode can be invoked to drop all dirty buffers of the inode in the near future.

val get_write_eof : plasma_cluster -> inode -> int64
Returns the designated new EOF value of pending writes. Raises Not_found if nothing is known.
val get_write_mtime : plasma_cluster -> inode -> Plasma_rpcapi_aux.time
Returns the designated new mtime value of pending writes. Raises Not_found if nothing is known.
val flush_e : plasma_cluster ->
inode -> int64 -> int64 -> unit Uq_engines.engine
val flush : plasma_cluster -> inode -> int64 -> int64 -> unit
flush_e inode pos len: Flushes all buffered data of inode from pos to pos+len-1, or to the end of the file if len=0. This ensures that data is really written.
val drop_inode : plasma_cluster -> inode -> unit
Drops all buffers of this inode, including dirty ones. This will prevent that these are again tried to be written, and it will free up buffer space.
val flush_all_e : plasma_cluster -> unit Uq_engines.engine
val flush_all : plasma_cluster -> unit
Flushes all buffers. (No error reporting, though.)
val snapshot_e : ?append:bool -> plasma_trans -> int64 -> unit Uq_engines.engine
val snapshot : ?append:bool -> plasma_trans -> int64 -> unit
snapshot trans inode: Takes a snapshot of the file, affecting buffered reads and writes, and a few other functions. Reads and writes use now the transaction trans instead of creating transactions automatically. Also, the block list is completely buffered up. The main effects:

  • Reads view the contents of the file in the version when the snapshot was made, even if other transactions change the file. Only the changes made via trans are visible. Taking a snapshot is an atomic operation.
  • Writes can change the file. However, there is no automatic commit anymore. First if trans is committed (by calling commit) the changes are made permanent (atomically).
Thus, snapshots can be used to read and write files with high consistency guarantees.

There are a few other effects of the snapshot mode:

  • At the moment the snapshot is made, all buffers for this inode are dropped. This affects both clean and dirty buffers.
  • When trans is aborted, the dirty buffers are also dropped.
  • When trans is committed, the buffers for inode remain intact, of course, because they reflect now the latest state of the file. Note that it is strongly recommended to flush the buffers before committing.
  • The flush operation can now fail with ECONFLICT if there are other transactions writing to the same file.
The snapshot ends when trans is either committed or aborted.

The following functions also see/modify the snapshot if trans is used:

  • get_inodeinfo
  • set_inodeinfo
  • truncate
  • get_write_eof
  • get_write_mtime
  • flush
  • flush_all
It is a bad idea to access the file via this client while the snapshot is being made.

The append flag enables an optimization if new data is only appended to the file. In this case, it is sufficient to take only a snapshot of the last block of the file, because the previous blocks can be considered as immutable.

Filename interface

Note that this module does not support tree prefixes. This means it must be just "/path", and not "plasma::/path". All path names need to be absolute.
val lookup_e : plasma_trans ->
string -> bool -> inode Uq_engines.engine
val lookup : plasma_trans -> string -> bool -> inode
Looks the absolute filename up and returns the inode number

The bool says whether to keep the last component of the path as symbolic link (lstat semantics).

val dir_lookup_e : plasma_trans ->
inode ->
string -> bool -> inode Uq_engines.engine
val dir_lookup : plasma_trans ->
inode -> string -> bool -> inode
Looks the filename up relative to a directory (given as inode) and returns the inode number. The filename can also be given as relative path.

If the filename is absolute the inode number is ignored.

The bool says whether to keep the last component of the path as symbolic link (lstat semantics).

dir_lookup trans inode "" _ is legal and just returns inode.

val rev_lookup_e : plasma_trans ->
inode -> string list Uq_engines.engine
val rev_lookup : plasma_trans -> inode -> string list
Returns the filenames linked with this inode number.
val rev_lookup_dir_e : plasma_trans -> inode -> string Uq_engines.engine
val rev_lookup_dir : plasma_trans -> inode -> string
Returns the abs filename linked with this inode number which must be a directory. The filename is read-locked (i.e. cannot be renamed or deleted by a competing transaction).

It is possible to get an `econflict error when the lock requirement cannot be satisfied.

val namelock_e : plasma_trans ->
inode -> string -> unit Uq_engines.engine
val namelock : plasma_trans -> inode -> string -> unit
namelock trans dir name: Acquires an existence lock on the member name of directory dir. name must not contain slashes.

A namelock prevents that the entry name of the directory dir can be moved or deleted. This protection lasts until the end of the transaction. If a concurrent transaction tries to move or delete the file, it will get an `econflict error.

It is not allowed to lock a not yet existing entry.

It is not prevented that the directory dir is moved, and thus it is possible that the absolute path of the protected file changes.

val link_count_e : plasma_trans -> inode -> int Uq_engines.engine
val link_count : plasma_trans -> inode -> int
Returns the number of links (also no locks)
val link_e : plasma_trans ->
string -> inode -> unit Uq_engines.engine
val link : plasma_trans -> string -> inode -> unit
Links a name with an inode

For directories there is the restriction that at most one name may be linked with the inode.

val link_at_e : plasma_trans ->
inode ->
string -> inode -> unit Uq_engines.engine
val link_at : plasma_trans ->
inode -> string -> inode -> unit
link_at trans dir_inode name inode: Adds the entry name into the directory dir_inode and connects the entry with inode. name must not contain slashes.
val unlink_e : plasma_trans -> string -> unit Uq_engines.engine
val unlink : plasma_trans -> string -> unit
Unlinks the name. If the count of links drops to 0 this also removes the inode.

This also works for directories! (They must be empty, of course.)

val unlink_at_e : plasma_trans ->
inode -> string -> unit Uq_engines.engine
val unlink_at : plasma_trans -> inode -> string -> unit
unlink_at trans dir_inode name: Removes the entry name from the directory dir_inode. name must not contain slashes.
val rename_e : plasma_trans -> string -> string -> unit Uq_engines.engine
val rename : plasma_trans -> string -> string -> unit
rename trans old_path new_path: Renames/moves the file or directory identified by old_path to the location identified by new_path. There must not be a file at new_path (i.e. you cannot move into a directory).
val rename_at_e : plasma_trans ->
inode ->
string -> inode -> string -> unit Uq_engines.engine
val rename_at : plasma_trans ->
inode -> string -> inode -> string -> unit
rename_at trans old_dir_inode old_name new_dir_inode new_name: Moves the file old_name in old_dir_inode to the new location which is given by new_name in new_dir_inode. Neither old_name nor new_name must contain slashes.
val list_inode_e : plasma_trans ->
inode -> (string * inode) list Uq_engines.engine
val list_inode : plasma_trans ->
inode -> (string * inode) list
Lists the contents of the directory, given by inode
val list_e : plasma_trans ->
string -> (string * inode) list Uq_engines.engine
val list : plasma_trans -> string -> (string * inode) list
Lists the contents of the directory, given by filename
val create_file_e : plasma_trans ->
string ->
Plasma_rpcapi_aux.inodeinfo -> inode Uq_engines.engine
val create_file : plasma_trans ->
string -> Plasma_rpcapi_aux.inodeinfo -> inode
Creates a regular file (inode plus name) or a symlink. The file type must be `ftype_regular or `ftype_symlink.
val mkdir_e : plasma_trans ->
string ->
Plasma_rpcapi_aux.inodeinfo -> inode Uq_engines.engine
val mkdir : plasma_trans ->
string -> Plasma_rpcapi_aux.inodeinfo -> inode
Creates a directory
val regular_ii : plasma_cluster -> int -> Plasma_rpcapi_aux.inodeinfo
regular_ii c mode: Creates an inodeinfo record for a new empty regular file, where the mode field is set to mode modulo the current mask
val symlink_ii : plasma_cluster -> string -> Plasma_rpcapi_aux.inodeinfo
regular_ii c target: Creates an inodeinfo record for a symlink pointing to target
val dir_ii : plasma_cluster -> int -> Plasma_rpcapi_aux.inodeinfo
regular_ii c mode: Creates an inodeinfo record for a new directory, where the mode field is set to mode modulo the current mask

Low-level functions

val get_blocklist_e : plasma_trans ->
inode ->
int64 -> int64 -> bool -> Plasma_rpcapi_aux.blockinfo list Uq_engines.engine
val get_blocklist : plasma_trans ->
inode ->
int64 -> int64 -> bool -> Plasma_rpcapi_aux.blockinfo list
get_blocklist_e t inode block n keep_flag Returns the list of blocks for blocks block to blocks+n-1. This is useful for analyzing where the blocks are actually physically stored.

If keep_flag the blocks are protected for the duration of the transaction.

Users and groups

val read_admin_table_e : plasma_cluster -> string -> string Uq_engines.engine
val read_admin_table : plasma_cluster -> string -> string
read_admin_table_e key Returns the admin table key as text. Possible keys: "passwd", "group".
val write_admin_table_e : plasma_cluster -> string -> string -> unit Uq_engines.engine
val write_admin_table : plasma_cluster -> string -> string -> unit
write_admin_table_e key file: Sets the admin table key to file. Possible keys: "passwd", "group".
val read_ug_admin_e : plasma_cluster -> Plasma_ug.ug_admin Uq_engines.engine
val read_ug_admin : plasma_cluster -> Plasma_ug.ug_admin
Read the admin tables for managing users and groups, and make the contents available as Plasma_ug.ug_admin object.
val write_ug_admin_e : plasma_cluster -> Plasma_ug.ug_admin -> unit Uq_engines.engine
val write_ug_admin : plasma_cluster -> Plasma_ug.ug_admin -> unit
Write the admin tables back (after modification)


val with_trans_e : plasma_cluster ->
(plasma_trans -> 'a Uq_engines.engine) -> 'a Uq_engines.engine
val with_trans : plasma_cluster -> (plasma_trans -> 'a) -> 'a
with_trans c f: Starts a new transaction t and runs f t. The transaction is committed if f returns normally, and aborted if f raises an exception.
val retry_e : plasma_cluster ->
string -> ('a -> 'b Uq_engines.engine) -> 'a -> 'b Uq_engines.engine
val retry : plasma_cluster -> string -> ('a -> 'b) -> 'a -> 'b
retry c name f arg: Executes f arg and returns the result. If an ECONFLICT error or timeout occurs the execution is repeated, until a general timeout is reached.

Errors are logged (Netlog). name is used in log output.

It is common to combine retry and with_trans, e.g.

         retry c "create_file"
           (fun filename ->
              with_trans c
                (fun trans ->
                   create_file trans filename (regular_ii c 0o666)

implementing the general convention that retry means to retry whole transactions.

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