%% ------------------------------------------------------------------- %% %% Copyright (c) 2007-2015 Basho Technologies, Inc. All Rights Reserved. %% %% This file is provided to you under the Apache License, %% Version 2.0 (the "License"); you may not use this file %% except in compliance with the License. You may obtain %% a copy of the License at %% %% http://www.apache.org/licenses/LICENSE-2.0 %% %% Unless required by applicable law or agreed to in writing, %% software distributed under the License is distributed on an %% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY %% KIND, either express or implied. See the License for the %% specific language governing permissions and limitations %% under the License. %% %% ------------------------------------------------------------------- %% @doc This is a proxy process which mediates access to Machi FLU %% controlled files. In particular, it manages the "write-once register" %% conceit at the heart of Machi's design. %% %% Read, write and append requests for a single file will be managed %% through this proxy. Clients can also request syncs for specific %% types of filehandles. %% %% As operations are requested, the proxy keeps track of how many %% operations it has performed (and how many errors were generated.) %% After a sufficient number of inactivity, the server terminates %% itself. %% %% TODO: %% 1. Some way to transition the proxy into a wedged state that %% doesn't rely on message delivery. %% %% 2. Check max file size on appends. Writes we take on faith we can %% and should handle. %% %% 3. Async checksum reads on startup. -module(machi_file_proxy). -behaviour(gen_server). -include("machi.hrl"). %% public API -export([ start_link/2, stop/1, sync/1, sync/2, read/3, write/3, write/4, append/2, append/4 ]). %% gen_server callbacks -export([ init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3 ]). -define(TICK, 30*1000). %% XXX FIXME Should be something like 5 seconds -define(TICK_THRESHOLD, 5). %% After this + 1 more quiescent ticks, shutdown -define(TIMEOUT, 10*1000). -define(TOO_MANY_ERRORS_RATIO, 50). -type op_stats() :: { Total :: non_neg_integer(), Errors :: non_neg_integer() }. -type byte_sequence() :: { Offset :: non_neg_integer(), Size :: pos_integer()|infinity }. -record(state, { data_dir :: string() | undefined, filename :: string() | undefined, data_path :: string() | undefined, wedged = false :: boolean(), csum_file :: string()|undefined, csum_path :: string()|undefined, eof_position = 0 :: non_neg_integer(), unwritten_bytes = [] :: [byte_sequence()], data_filehandle :: file:filehandle(), csum_table :: machi_csum_table:table(), tref :: reference(), %% timer ref ticks = 0 :: non_neg_integer(), %% ticks elapsed with no new operations ops = 0 :: non_neg_integer(), %% sum of all ops reads = {0, 0} :: op_stats(), writes = {0, 0} :: op_stats(), appends = {0, 0} :: op_stats() }). %% Public API % @doc Start a new instance of the file proxy service. Takes the filename % and data directory as arguments. This function is typically called by the % `machi_file_proxy_sup:start_proxy/2' function. -spec start_link(Filename :: string(), DataDir :: string()) -> any(). start_link(Filename, DataDir) -> gen_server:start_link(?MODULE, {Filename, DataDir}, []). % @doc Request to stop an instance of the file proxy service. -spec stop(Pid :: pid()) -> ok. stop(Pid) when is_pid(Pid) -> gen_server:call(Pid, {stop}, ?TIMEOUT). % @doc Force a sync of all filehandles -spec sync(Pid :: pid()) -> ok|{error, term()}. sync(Pid) when is_pid(Pid) -> sync(Pid, all); sync(_Pid) -> lager:warning("Bad pid to sync"), {error, bad_arg}. % @doc Force a sync of a specific filehandle type. Valid types are `all', `csum' and `data'. -spec sync(Pid :: pid(), Type :: all|data|csum) -> ok|{error, term()}. sync(Pid, Type) when is_pid(Pid) andalso ( Type =:= all orelse Type =:= csum orelse Type =:= data ) -> gen_server:call(Pid, {sync, Type}, ?TIMEOUT); sync(_Pid, Type) -> lager:warning("Bad arg to sync: Type ~p", [Type]), {error, bad_arg}. % @doc Read file at offset for length -spec read(Pid :: pid(), Offset :: non_neg_integer(), Length :: non_neg_integer()) -> {ok, Data :: binary(), Checksum :: binary()} | {error, Reason :: term()}. read(Pid, Offset, Length) when is_pid(Pid) andalso is_integer(Offset) andalso Offset >= 0 andalso is_integer(Length) andalso Length > 0 -> gen_server:call(Pid, {read, Offset, Length}, ?TIMEOUT); read(_Pid, Offset, Length) -> lager:warning("Bad args to read: Offset ~p, Length ~p", [Offset, Length]), {error, bad_arg}. % @doc Write data at offset -spec write(Pid :: pid(), Offset :: non_neg_integer(), Data :: binary()) -> ok|{error, term()}. write(Pid, Offset, Data) when is_pid(Pid) andalso is_integer(Offset) andalso Offset >= 0 andalso is_binary(Data) -> write(Pid, Offset, [], Data); write(_Pid, Offset, _Data) -> lager:warning("Bad arg to write: Offset ~p", [Offset]), {error, bad_arg}. % @doc Write data at offset, including the client metadata. ClientMeta is a proplist % that expects the following keys and values: % -spec write(Pid :: pid(), Offset :: non_neg_integer(), ClientMeta :: proplists:proplist(), Data :: binary()) -> ok|{error, term()}. write(Pid, Offset, ClientMeta, Data) when is_pid(Pid) andalso is_integer(Offset) andalso Offset >= 0 andalso is_list(ClientMeta) andalso is_binary(Data) -> gen_server:call(Pid, {write, Offset, ClientMeta, Data}, ?TIMEOUT); write(_Pid, Offset, ClientMeta, _Data) -> lager:warning("Bad arg to write: Offset ~p, ClientMeta: ~p", [Offset, ClientMeta]), {error, bad_arg}. % @doc Append data -spec append(Pid :: pid(), Data :: binary()) -> {ok, File :: string(), Offset :: non_neg_integer()} |{error, term()}. append(Pid, Data) when is_pid(Pid) andalso is_binary(Data) -> append(Pid, [], 0, Data); append(_Pid, _Data) -> lager:warning("Bad arguments to append/2"), {error, bad_arg}. % @doc Append data to file, supplying client metadata and (if desired) a % reservation for additional space. ClientMeta is a proplist and expects the % same keys as write/4. -spec append(Pid :: pid(), ClientMeta :: proplists:proplist(), Extra :: non_neg_integer(), Data :: binary()) -> {ok, File :: string(), Offset :: non_neg_integer()} |{error, term()}. append(Pid, ClientMeta, Extra, Data) when is_pid(Pid) andalso is_list(ClientMeta) andalso is_integer(Extra) andalso Extra >= 0 andalso is_binary(Data) -> gen_server:call(Pid, {append, ClientMeta, Extra, Data}, ?TIMEOUT); append(_Pid, ClientMeta, Extra, _Data) -> lager:warning("Bad arg to append: ClientMeta ~p, Extra ~p", [ClientMeta, Extra]), {error, bad_arg}. %% gen_server callbacks % @private init({Filename, DataDir}) -> CsumFile = machi_util:make_checksum_filename(DataDir, Filename), {_, DPath} = machi_util:make_data_filename(DataDir, Filename), ok = filelib:ensure_dir(CsumFile), ok = filelib:ensure_dir(DPath), {ok, CsumTable} = machi_csum_table:open(CsumFile, []), UnwrittenBytes = machi_csum_table:calc_unwritten_bytes(CsumTable), {Eof, infinity} = lists:last(UnwrittenBytes), {ok, FHd} = file:open(DPath, [read, write, binary, raw]), Tref = schedule_tick(), St = #state{ filename = Filename, data_dir = DataDir, data_path = DPath, csum_file = CsumFile, data_filehandle = FHd, csum_table = CsumTable, tref = Tref, unwritten_bytes = UnwrittenBytes, eof_position = Eof}, lager:debug("Starting file proxy ~p for filename ~p, state = ~p", [self(), Filename, St]), {ok, St}. % @private handle_call({stop}, _From, State) -> lager:debug("Requested to stop."), {stop, normal, State}; handle_call({sync, data}, _From, State = #state{ data_filehandle = FHd }) -> R = file:sync(FHd), {reply, R, State}; handle_call({sync, csum}, _From, State = #state{ csum_table = T }) -> R = machi_csum_table:sync(T), {reply, R, State}; handle_call({sync, all}, _From, State = #state{filename = F, data_filehandle = FHd, csum_table = T }) -> R = machi_csum_table:sync(T), R1 = file:sync(FHd), Resp = case {R, R1} of {ok, ok} -> ok; {ok, O1} -> lager:error("Got ~p during a data file sync on file ~p", [O1, F]), O1; {O2, ok} -> lager:error("Got ~p during a csum file sync on file ~p", [O2, F]), O2; {O3, O4} -> lager:error("Got ~p ~p syncing all files for file ~p", [O3, O4, F]), {O3, O4} end, {reply, Resp, State}; %%% READS handle_call({read, _Offset, _Length}, _From, State = #state{wedged = true, reads = {T, Err} }) -> {reply, {error, wedged}, State#state{writes = {T + 1, Err + 1}}}; handle_call({read, Offset, Length}, _From, State = #state{eof_position = Eof, reads = {T, Err} }) when Offset + Length > Eof -> lager:error("Read request at offset ~p for ~p bytes is past the last write offset of ~p", [Offset, Length, Eof]), {reply, {error, not_written}, State#state{reads = {T + 1, Err + 1}}}; handle_call({read, Offset, Length}, _From, State = #state{filename = F, data_filehandle = FH, csum_table = CsumTable, unwritten_bytes = U, reads = {T, Err} }) -> Checksum = case machi_csum_table:find(CsumTable, Offset, Length) of {ok, Checksum0} -> Checksum0; _ -> undefined end, {Resp, NewErr} = case handle_read(FH, F, Checksum, Offset, Length, U) of {ok, Bytes, Csum} -> {{ok, Bytes, Csum}, Err}; eof -> {{error, not_written}, Err + 1}; Error -> {Error, Err + 1} end, {reply, Resp, State#state{reads = {T+1, NewErr}}}; %%% WRITES handle_call({write, _Offset, _ClientMeta, _Data}, _From, State = #state{wedged = true, writes = {T, Err} }) -> {reply, {error, wedged}, State#state{writes = {T + 1, Err + 1}}}; handle_call({write, Offset, ClientMeta, Data}, _From, State = #state{unwritten_bytes = U, filename = F, writes = {T, Err}, data_filehandle = FHd, csum_table = CsumTable }) -> ClientCsumTag = proplists:get_value(client_csum_tag, ClientMeta, ?CSUM_TAG_NONE), ClientCsum = proplists:get_value(client_csum, ClientMeta, <<>>), {Resp, NewErr, NewU} = case check_or_make_tagged_csum(ClientCsumTag, ClientCsum, Data) of {error, {bad_csum, Bad}} -> lager:error("Bad checksum on write; client sent ~p, we computed ~p", [ClientCsum, Bad]), {{error, bad_checksum}, Err + 1, U}; TaggedCsum -> case handle_write(FHd, CsumTable, F, TaggedCsum, Offset, Data, U) of {ok, NewU1} -> {ok, Err, NewU1}; Error -> {Error, Err + 1, U} end end, {NewEof, infinity} = lists:last(NewU), {reply, Resp, State#state{writes = {T+1, NewErr}, eof_position = NewEof, unwritten_bytes = NewU }}; %% APPENDS handle_call({append, _ClientMeta, _Extra, _Data}, _From, State = #state{wedged = true, appends = {T, Err} }) -> {reply, {error, wedged}, State#state{appends = {T+1, Err+1}}}; handle_call({append, ClientMeta, Extra, Data}, _From, State = #state{eof_position = EofP, unwritten_bytes = U, filename = F, appends = {T, Err}, data_filehandle = FHd, csum_table = CsumTable }) -> ClientCsumTag = proplists:get_value(client_csum_tag, ClientMeta, ?CSUM_TAG_NONE), ClientCsum = proplists:get_value(client_csum, ClientMeta, <<>>), {Resp, NewErr, NewU} = case check_or_make_tagged_csum(ClientCsumTag, ClientCsum, Data) of {error, {bad_csum, Bad}} -> lager:error("Bad checksum; client sent ~p, we computed ~p", [ClientCsum, Bad]), {{error, bad_checksum}, Err + 1, U}; TaggedCsum -> case handle_write(FHd, CsumTable, F, TaggedCsum, EofP, Data, U) of {ok, NewU1} -> {{ok, F, EofP}, Err, NewU1}; Error -> {Error, Err + 1, EofP, U} end end, {NewEof, infinity} = lists:last(NewU), {reply, Resp, State#state{appends = {T+1, NewErr}, eof_position = NewEof + Extra, unwritten_bytes = NewU }}; handle_call(Req, _From, State) -> lager:warning("Unknown call: ~p", [Req]), {reply, whoaaaaaaaaaaaa, State}. % @private handle_cast(Cast, State) -> lager:warning("Unknown cast: ~p", [Cast]), {noreply, State}. % @private handle_info(tick, State = #state{eof_position = Eof}) when Eof >= ?MAX_FILE_SIZE -> lager:notice("Eof position ~p >= max file size ~p. Shutting down.", [Eof, ?MAX_FILE_SIZE]), {stop, file_rollover, State}; %% XXX Is this a good idea? Need to think this through a bit. handle_info(tick, State = #state{wedged = true}) -> {stop, wedged, State}; %% I dunno. This may not be a good idea, but it seems like if we're throwing lots of %% errors, we ought to shut down and give up our file descriptors. handle_info(tick, State = #state{ ops = Ops, reads = {RT, RE}, writes = {WT, WE}, appends = {AT, AE} }) when Ops > 100 andalso trunc(((RE+WE+AE) / RT+WT+AT) * 100) > ?TOO_MANY_ERRORS_RATIO -> Errors = RE + WE + AE, lager:notice("Got ~p errors. Shutting down.", [Errors]), {stop, too_many_errors, State}; handle_info(tick, State = #state{ ticks = Ticks, ops = Ops, reads = {RT, _RE}, writes = {WT, _WE}, appends = {AT, _AE}}) when Ops == RT + WT + AT, Ticks == ?TICK_THRESHOLD -> lager:debug("Got 5 ticks with no new activity. Shutting down."), {stop, normal, State}; handle_info(tick, State = #state{ ticks = Ticks, ops = Ops, reads = {RT, _RE}, writes = {WT, _WE}, appends = {AT, _AE}}) when Ops == RT + WT + AT -> lager:debug("No new activity since last tick. Incrementing tick counter."), Tref = schedule_tick(), {noreply, State#state{tref = Tref, ticks = Ticks + 1}}; handle_info(tick, State = #state{ reads = {RT, _RE}, writes = {WT, _WE}, appends = {AT, _AE} }) -> Ops = RT + WT + AT, lager:debug("Setting ops counter to ~p", [Ops]), Tref = schedule_tick(), {noreply, State#state{tref = Tref, ops = Ops}}; %handle_info({wedged, EpochId} State = #state{epoch = E}) when E /= EpochId -> % lager:notice("Wedge epoch ~p but ignoring because our epoch id is ~p", [EpochId, E]), % {noreply, State}; %handle_info({wedged, EpochId}, State = #state{epoch = E}) when E == EpochId -> % lager:notice("Wedge epoch ~p same as our epoch id ~p; we are wedged. Bummer.", [EpochId, E]), % {noreply, State#state{wedged = true}}; % flu1.erl: % ProxyPid = get_proxy_pid(Filename), % Are we wedged? if not % machi_file_proxy:read(Pid, Offset, Length) % otherwise -> error,wedged % % get_proxy_pid(Filename) -> % Pid = lookup_pid(Filename) % is_pid_alive(Pid) % Pid % if not alive then start one handle_info(Req, State) -> lager:warning("Unknown info message: ~p", [Req]), {noreply, State}. % @private terminate(Reason, #state{filename = F, data_filehandle = FHd, csum_table = T, reads = {RT, RE}, writes = {WT, WE}, appends = {AT, AE} }) -> lager:info("Shutting down proxy for file ~p because ~p", [F, Reason]), lager:info(" Op Tot/Error", []), lager:info(" Reads: ~p/~p", [RT, RE]), lager:info(" Writes: ~p/~p", [WT, WE]), lager:info("Appends: ~p/~p", [AT, AE]), ok = file:sync(FHd), ok = file:close(FHd), ok = machi_csum_table:sync(T), ok = machi_csum_table:close(T), ok. % @private code_change(_OldVsn, State, _Extra) -> {ok, State}. %% Private functions -spec schedule_tick() -> reference(). schedule_tick() -> erlang:send_after(?TICK, self(), tick). -spec check_or_make_tagged_csum(Type :: binary(), Checksum :: binary(), Data :: binary() ) -> binary() | {error, {bad_csum, Bad :: binary()}}. check_or_make_tagged_csum(?CSUM_TAG_NONE, _Csum, Data) -> %% We are making a checksum here Csum = machi_util:checksum_chunk(Data), machi_util:make_tagged_csum(server_sha, Csum); check_or_make_tagged_csum(Tag, InCsum, Data) when Tag == ?CSUM_TAG_CLIENT_SHA; Tag == ?CSUM_TAG_SERVER_SHA -> Csum = machi_util:checksum_chunk(Data), case Csum =:= InCsum of true -> machi_util:make_tagged_csum(server_sha, Csum); false -> {error, {bad_csum, Csum}} end; check_or_make_tagged_csum(OtherTag, _ClientCsum, _Data) -> lager:warning("Unknown checksum tag ~p", [OtherTag]), {error, bad_checksum}. -spec handle_read(FHd :: file:filehandle(), Filename :: string(), TaggedCsum :: undefined|binary(), Offset :: non_neg_integer(), Size :: non_neg_integer(), Unwritten :: [byte_sequence()] ) -> {ok, Bytes :: binary(), Csum :: binary()} | eof | {error, bad_checksum} | {error, partial_read} | {error, not_written} | {error, Other :: term() }. % @private Attempt a read operation on the given offset and length. %
  • % % % % % %
    • % % On success, `{ok, Bytes, Checksum}' is returned. handle_read(FHd, Filename, undefined, Offset, Size, U) -> handle_read(FHd, Filename, machi_util:make_tagged_csum(none), Offset, Size, U); handle_read(FHd, Filename, TaggedCsum, Offset, Size, U) -> case is_byte_range_unwritten(Offset, Size, U) of true -> {error, not_written}; false -> do_read(FHd, Filename, TaggedCsum, Offset, Size) end. do_read(FHd, Filename, TaggedCsum, Offset, Size) -> case file:pread(FHd, Offset, Size) of eof -> eof; {ok, Bytes} when byte_size(Bytes) == Size -> {Tag, Ck} = machi_util:unmake_tagged_csum(TaggedCsum), case check_or_make_tagged_csum(Tag, Ck, Bytes) of {error, Bad} -> lager:error("Bad checksum; got ~p, expected ~p", [Bad, Ck]), {error, bad_checksum}; TaggedCsum -> {ok, Bytes, TaggedCsum}; %% XXX FIXME: Should we return something other than %% {ok, ....} in this case? OtherCsum when Tag =:= ?CSUM_TAG_NONE -> {ok, Bytes, OtherCsum} end; {ok, Partial} -> lager:error("In file ~p, offset ~p, wanted to read ~p bytes, but got ~p", [Filename, Offset, Size, byte_size(Partial)]), {error, partial_read}; Other -> lager:error("While reading file ~p, offset ~p, length ~p, got ~p", [Filename, Offset, Size, Other]), {error, Other} end. -spec handle_write( FHd :: file:filehandle(), CsumTable :: machi_csum_table:table(), Filename :: string(), TaggedCsum :: binary(), Offset :: non_neg_integer(), Data :: binary(), Unwritten :: [byte_sequence()] ) -> {ok, NewU :: [byte_sequence()]} | {error, written} | {error, Reason :: term()}. % @private Implements the write and append operation. The first task is to % determine if the offset and data size has been written. If not, the write % is allowed proceed. A special case is made when an offset and data size % match a checksum. In that case we read the data off the disk, validate the % checksum and return a "fake" ok response as if the write had been performed % when it hasn't really. % % If a write proceeds, the offset, size and checksum are written to a metadata % file, and the internal list of unwritten bytes is modified to reflect the % just-performed write. This is then returned to the caller as % `{ok, NewUnwritten}' where NewUnwritten is the revised unwritten byte list. handle_write(FHd, CsumTable, Filename, TaggedCsum, Offset, Data, U) -> Size = iolist_size(Data), case is_byte_range_unwritten(Offset, Size, U) of false -> case machi_csum_table:find(CsumTable, Offset, Size) of {error, trimmed} = Error -> Error; {error, unknown_chunk} -> %% The specified has some bytes written, while %% it's not in the checksum table. Trust U and %% return as it is used. {error, written}; {ok, TaggedCsum} -> case do_read(FHd, Filename, TaggedCsum, Offset, Size) of eof -> lager:warning("This should never happen: got eof while reading at offset ~p in file ~p that's supposedly written", [Offset, Filename]), {error, server_insanity}; {ok, _, _} -> {ok, U}; _ -> {error, written} end; {ok, OtherCsum} -> %% Got a checksum, but it doesn't match the data block's lager:error("During a potential write at offset ~p in file ~p, a check for unwritten bytes gave us checksum ~p but the data we were trying to trying to write has checksum ~p", [Offset, Filename, OtherCsum, TaggedCsum]), {error, written} end; true -> try do_write(FHd, CsumTable, Filename, TaggedCsum, Offset, Size, Data, U) catch %%% XXX FIXME: be more specific on badmatch that might %%% occur around line 593 when we write the checksum %%% file entry for the data blob we just put on the disk error:Reason -> {error, Reason} end end. % @private Implements the disk writes for both the write and append % operation. -spec do_write( FHd :: file:descriptor(), CsumTable :: machi_csum_table:table(), Filename :: string(), TaggedCsum :: binary(), Offset :: non_neg_integer(), Size :: non_neg_integer(), Data :: binary(), Unwritten :: [byte_sequence()] ) -> {ok, NewUnwritten :: [byte_sequence()]} | {error, Reason :: term()}. do_write(FHd, CsumTable, Filename, TaggedCsum, Offset, Size, Data, U) -> case file:pwrite(FHd, Offset, Data) of ok -> lager:debug("Successful write in file ~p at offset ~p, length ~p", [Filename, Offset, Size]), ok = machi_csum_table:write(CsumTable, Offset, Size, TaggedCsum), NewU = update_unwritten(Offset, Size, U), lager:debug("Successful write to checksum file for ~p; unwritten bytes are now: ~p", [Filename, NewU]), {ok, NewU}; Other -> lager:error("Got ~p during write to file ~p at offset ~p, length ~p", [Other, Filename, Offset, Size]), {error, Other} end. -spec is_byte_range_unwritten( Offset :: non_neg_integer(), Size :: pos_integer(), Unwritten :: [byte_sequence()] ) -> boolean(). % @private Given an offset and a size, return `true' if a byte range has % not been written. Otherwise, return `false'. is_byte_range_unwritten(Offset, Size, Unwritten) -> case Unwritten of [] -> lager:critical("Unwritten byte list has 0 entries! This should never happen."), false; [{Eof, infinity}] -> Offset >= Eof; _ -> case lookup_unwritten(Offset, Size, Unwritten) of {ok, _} -> true; not_found -> false end end. -spec lookup_unwritten( Offset :: non_neg_integer(), Size :: pos_integer(), Unwritten :: [byte_sequence()] ) -> {ok, byte_sequence()} | not_found. % @private Given an offset and a size, scan the list of unwritten bytes and % look for a "hole" where a write might be allowed if any exist. If a % suitable byte sequence is found, the function returns a tuple of {ok, % {Position, Space}} is returned. `not_found' is returned if no suitable % space is located. lookup_unwritten(_Offset, _Size, []) -> not_found; lookup_unwritten(Offset, _Size, [H={Pos, infinity}|_Rest]) when Offset >= Pos -> {ok, H}; lookup_unwritten(Offset, Size, [H={Pos, Space}|_Rest]) when Offset >= Pos andalso Offset < Pos+Space andalso Size =< (Space - (Offset - Pos)) -> {ok, H}; lookup_unwritten(Offset, Size, [_H|Rest]) -> %% These are not the droids you're looking for. lookup_unwritten(Offset, Size, Rest). %%% if the pos is greater than offset + size then we're done. End early. -spec update_unwritten( Offset :: non_neg_integer(), Size :: pos_integer(), Unwritten :: [byte_sequence()] ) -> NewUnwritten :: [byte_sequence()]. % @private Given an offset, a size and the unwritten byte list, return an updated % and sorted unwritten byte list accounting for any completed write operation. update_unwritten(Offset, Size, Unwritten) -> case lookup_unwritten(Offset, Size, Unwritten) of not_found -> lager:error("Couldn't find byte sequence tuple for a write which earlier found a valid spot to write!!! This should never happen!"), Unwritten; {ok, {Offset, Size}} -> %% we neatly filled in our hole... lists:keydelete(Offset, 1, Unwritten); {ok, S={Pos, _}} -> lists:sort(lists:keydelete(Pos, 1, Unwritten) ++ update_byte_range(Offset, Size, S)) end. -spec update_byte_range( Offset :: non_neg_integer(), Size :: pos_integer(), Sequence :: byte_sequence() ) -> Updates :: [byte_sequence()]. % @private Given an offset and size and a byte sequence tuple where a % write took place, return a list of updates to the list of unwritten bytes % accounting for the space occupied by the just completed write. update_byte_range(Offset, Size, {Eof, infinity}) when Offset == Eof -> [{Offset + Size, infinity}]; update_byte_range(Offset, Size, {Eof, infinity}) when Offset > Eof -> [{Eof, (Offset - Eof)}, {Offset+Size, infinity}]; update_byte_range(Offset, Size, {Pos, Space}) when Offset == Pos andalso Size < Space -> [{Offset + Size, Space - Size}]; update_byte_range(Offset, Size, {Pos, Space}) when Offset > Pos -> [{Pos, Offset - Pos}, {Offset+Size, ( (Pos+Space) - (Offset + Size) )}].