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authorJoseph Blomstedt <[email protected]>2012-11-29 14:50:42 -0800
committerSteve Vinoski <[email protected]>2013-11-15 10:19:19 -0500
commitf47c818746c1df4055b1de8aabf47364f502274c (patch)
treea85d3ba3585a4bf29d01c3d6a7d43f0b75bab9f4 /erts/emulator/drivers
parentc01df2215ac3ddef82116abac5eaf236d3788f21 (diff)
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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.
Diffstat (limited to 'erts/emulator/drivers')
-rw-r--r--erts/emulator/drivers/common/erl_efile.h1
-rw-r--r--erts/emulator/drivers/unix/unix_efile.c9
-rw-r--r--erts/emulator/drivers/win32/win_efile.c7
3 files changed, 16 insertions, 1 deletions
diff --git a/erts/emulator/drivers/common/erl_efile.h b/erts/emulator/drivers/common/erl_efile.h
index 5387f75efc..95c036db8f 100644
--- a/erts/emulator/drivers/common/erl_efile.h
+++ b/erts/emulator/drivers/common/erl_efile.h
@@ -34,6 +34,7 @@
#define EFILE_COMPRESSED 8
#define EFILE_MODE_EXCL 16
#define EFILE_NO_TRUNCATE 32 /* Special for reopening on VxWorks */
+#define EFILE_MODE_SYNC 64
/*
* Seek modes for efile_seek().
diff --git a/erts/emulator/drivers/unix/unix_efile.c b/erts/emulator/drivers/unix/unix_efile.c
index 55539b44dd..8ffc05da99 100644
--- a/erts/emulator/drivers/unix/unix_efile.c
+++ b/erts/emulator/drivers/unix/unix_efile.c
@@ -405,6 +405,15 @@ efile_openfile(Efile_error* errInfo, /* Where to return error codes. */
mode |= O_EXCL;
}
+ if (flags & EFILE_MODE_SYNC) {
+#ifdef O_SYNC
+ mode |= O_SYNC;
+#else
+ errno = ENOTSUP;
+ return check_error(-1, errInfo);
+#endif
+ }
+
fd = open(name, mode, FILE_MODE);
if (!check_error(fd, errInfo))
diff --git a/erts/emulator/drivers/win32/win_efile.c b/erts/emulator/drivers/win32/win_efile.c
index 319065f57b..d693d7d593 100644
--- a/erts/emulator/drivers/win32/win_efile.c
+++ b/erts/emulator/drivers/win32/win_efile.c
@@ -698,6 +698,7 @@ efile_openfile(Efile_error* errInfo, /* Where to return error codes. */
HANDLE fd; /* Handle to open file. */
DWORD access; /* Access mode: GENERIC_READ, GENERIC_WRITE. */
DWORD crFlags;
+ DWORD flagsAndAttrs = FILE_ATTRIBUTE_NORMAL;
WCHAR *wname = (WCHAR *) name;
switch (flags & (EFILE_MODE_READ|EFILE_MODE_WRITE)) {
@@ -719,6 +720,10 @@ efile_openfile(Efile_error* errInfo, /* Where to return error codes. */
return 0;
}
+ if (flags & EFILE_MODE_SYNC) {
+ flagsAndAttrs = FILE_FLAG_WRITE_THROUGH;
+ }
+
if (flags & EFILE_MODE_APPEND) {
crFlags = OPEN_ALWAYS;
}
@@ -727,7 +732,7 @@ efile_openfile(Efile_error* errInfo, /* Where to return error codes. */
}
fd = CreateFileW(wname, access,
FILE_SHARE_FLAGS,
- NULL, crFlags, FILE_ATTRIBUTE_NORMAL, NULL);
+ NULL, crFlags, flagsAndAttrs, NULL);
/*
* Check for errors.