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package tar-mirage
Module Tar_mirage.Make_KV_RWSource
Construct a read-write key-value store from an existing block device containing tar-format data. Note that it is append-only meaning removing or renaming files is currently unsupported and will return an error.
Parameters
module BLOCK : Mirage_block.SSignature
include Mirage_kv.RW
Read-write Stores
The functions set and remove will cause a flush in the underlying storage layer every time, which can degrade performance.
include Mirage_kv.RO
Read-only key-value stores
The type for errors.
The type representing the internal state of the key-value store.
Disconnect from the key-value store. While this might take some time to complete, it can never result in an error.
The type for keys.
exists t k is Some `Value if k is bound to a value in t, Some `Dictionary if k is a prefix of a valid key in t and None if no key with that prefix exists in t.
exists answers two questions: does the key exist and is it referring to a value or a dictionary.
An error occurs when the underlying storage layer fails.
get t k is the value bound to k in t.
The result is Error (`Value_expected k) if k refers to a dictionary in t.
Source
val get_partial :
t ->
key ->
offset:Optint.Int63.t ->
length:int ->
(string, error) result Lwt.tget_partial t k ~offset ~length is the length bytes wide value bound at offset of k in t.
If the size of k is less than offset, get_partial returns an empty string. If the size of k is less than offset+length, get_partial returns a short string. The result is Error (`Value_expected k) if k refers to a dictionary in t.
list t k is the list of entries and their types in the dictionary referenced by k in t. The returned keys are all absolute (i.e. Key.add k entry).
The result is Error (`Dictionary_expected k) if k refers to a value in t.
last_modified t k is the last time the value bound to k in t has been modified.
When the value bound to k is a dictionary, the implementation is free to decide how to compute a last modified timestamp, or return Error (`Value_expected _).
digest t k is the unique digest of the value bound to k in t.
When the value bound to k is a dictionary, the implementation is allowed to return Error (`Value_expected _). Otherwise, the digest is a unique and deterministic digest of its entries.
The type for write errors.
The pretty-printer for pp_write_error.
Source
val allocate :
t ->
key ->
?last_modified:Ptime.t ->
Optint.Int63.t ->
(unit, write_error) result Lwt.tallocate t key ~last_modified size allocates space for key in t with the provided size and last_modified. This is useful for e.g. append-only backends that could still use set_partial. The data will be filled with 0. If key already exists, Error (`Already_present key) is returned. If there's not enough space, Error `No_space is returned.
set t k v replaces the binding k -> v in t.
Durability is guaranteed.
Source
val set_partial :
t ->
key ->
offset:Optint.Int63.t ->
string ->
(unit, write_error) result Lwt.tset_partial t k offset v attempts to write v at offset in the value bound to k in t. If k contains directories that do not exist, set_partial will attempt to create them. If the size of k is less than offset, set_partial appends v at the end of k. If the size of k is greater than offset+length of v, set_partial leaves the last bytes of k unchanged.
The result is Error (`Value_expected k) if k refers to a dictionary in t.
remove t k removes any binding of k in t. If k was bound to a dictionary, the full dictionary will be removed.
Durability is guaranteed.
rename t source dest rename source to dest in t. If source and dest are both bound to values in t, dest is removed and the binding of source is moved to dest. If dest is bound to a dictionary in t, source is moved inside dest. If source is bound to a dictionary, the full dictionary is moved.
The result is Error (`Not_found source) if source does not exists in t. The result is Error (`Value_expected source) if source is bound to a dictionary in t and dest is bound to a value in t. The result id Error (`Rename_source_prefix (source, dest)) if source is a prefix of dest, and source is a directory.
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