From f47c818746c1df4055b1de8aabf47364f502274c Mon Sep 17 00:00:00 2001 From: Joseph Blomstedt Date: Thu, 29 Nov 2012 14:50:42 -0800 Subject: Add sync option to file:open/2 The sync option adds the POSIX O_SYNC flag to the open system call on platforms that support the flag or its equivalent, e.g., FILE_FLAG_WRITE_THROUGH on Windows. For platforms that don't support it, file:open/2 returns {error, enotsup} if the sync option is passed in. The semantics of O_SYNC are platform-specific. For example, not all platforms guarantee that all file metadata are written to the disk along with the file data when the flag is in effect. This issue is noted in the documentation this commit adds for the sync option. Add a test for the sync option. Note however that the underlying OS semantics for O_SYNC can't be tested automatically in any practical way, so the test assumes the OS does the right thing with the flag when present. For manual verification, dtruss on OS X and strace on Linux were both run against beam processes to watch calls to open(), and file:open/2 was called in Erlang shells to open files for writing, both with and without the sync option. Both the dtruss output and the strace output showed that the O_SYNC flag was present in the open() calls when sync was specified and was clear when sync was not specified. --- erts/preloaded/src/prim_file.erl | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'erts/preloaded/src/prim_file.erl') diff --git a/erts/preloaded/src/prim_file.erl b/erts/preloaded/src/prim_file.erl index 489e8ca4ea..5999e98340 100644 --- a/erts/preloaded/src/prim_file.erl +++ b/erts/preloaded/src/prim_file.erl @@ -123,9 +123,11 @@ -define(EFILE_MODE_APPEND, 4). -define(EFILE_COMPRESSED, 8). -define(EFILE_MODE_EXCL, 16). +%% Note: bit 5 (32) is used internally for VxWorks +-define(EFILE_MODE_SYNC, 64). %% Use this mask to get just the mode bits to be passed to the driver. --define(EFILE_MODE_MASK, 31). +-define(EFILE_MODE_MASK, 127). %% Seek modes for the driver's seek function. -define(EFILE_SEEK_SET, 0). @@ -1197,6 +1199,8 @@ open_mode([append|Rest], Mode, Portopts, Setopts) -> Portopts, Setopts); open_mode([exclusive|Rest], Mode, Portopts, Setopts) -> open_mode(Rest, Mode bor ?EFILE_MODE_EXCL, Portopts, Setopts); +open_mode([sync|Rest], Mode, Portopts, Setopts) -> + open_mode(Rest, Mode bor ?EFILE_MODE_SYNC, Portopts, Setopts); open_mode([delayed_write|Rest], Mode, Portopts, Setopts) -> open_mode([{delayed_write, 64*1024, 2000}|Rest], Mode, Portopts, Setopts); -- cgit v1.2.3