git/compat/win32/flush.c
Neeraj Singh abf38abec2 core.fsyncmethod: add writeout-only mode
This commit introduces the `core.fsyncMethod` configuration
knob, which can currently be set to `fsync` or `writeout-only`.

The new writeout-only mode attempts to tell the operating system to
flush its in-memory page cache to the storage hardware without issuing a
CACHE_FLUSH command to the storage controller.

Writeout-only fsync is significantly faster than a vanilla fsync on
common hardware, since data is written to a disk-side cache rather than
all the way to a durable medium. Later changes in this patch series will
take advantage of this primitive to implement batching of hardware
flushes.

When git_fsync is called with FSYNC_WRITEOUT_ONLY, it may fail and the
caller is expected to do an ordinary fsync as needed.

On Apple platforms, the fsync system call does not issue a CACHE_FLUSH
directive to the storage controller. This change updates fsync to do
fcntl(F_FULLFSYNC) to make fsync actually durable. We maintain parity
with existing behavior on Apple platforms by setting the default value
of the new core.fsyncMethod option.

Signed-off-by: Neeraj Singh <neerajsi@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-03-10 15:10:22 -08:00

29 lines
688 B
C

#include "git-compat-util.h"
#include <winternl.h>
#include "lazyload.h"
int win32_fsync_no_flush(int fd)
{
IO_STATUS_BLOCK io_status;
#define FLUSH_FLAGS_FILE_DATA_ONLY 1
DECLARE_PROC_ADDR(ntdll.dll, NTSTATUS, NTAPI, NtFlushBuffersFileEx,
HANDLE FileHandle, ULONG Flags, PVOID Parameters, ULONG ParameterSize,
PIO_STATUS_BLOCK IoStatusBlock);
if (!INIT_PROC_ADDR(NtFlushBuffersFileEx)) {
errno = ENOSYS;
return -1;
}
memset(&io_status, 0, sizeof(io_status));
if (NtFlushBuffersFileEx((HANDLE)_get_osfhandle(fd), FLUSH_FLAGS_FILE_DATA_ONLY,
NULL, 0, &io_status)) {
errno = EINVAL;
return -1;
}
return 0;
}