Merge branch 'ns/core-fsyncmethod' into ps/fsync-refs

* ns/core-fsyncmethod:
  core.fsync: documentation and user-friendly aggregate options
  core.fsync: new option to harden the index
  core.fsync: add configuration parsing
  core.fsync: introduce granular fsync control infrastructure
  core.fsyncmethod: add writeout-only mode
  wrapper: make inclusion of Windows csprng header tightly scoped

diff --cc cache.h
Simple merge

diff --cc config.c
Simple merge

diff --cc environment.c
Simple merge

diff --cc git-compat-util.h
index e50e2fafaec9d7cf378495bbf80af95cbb3d1d54,00356476a9d1dc5ea49f1e3c8ca59015311f080a..0892e209a2fb23f797030dd04c62cd534e3d1775
--- 1/git-compat-util.h
--- 2/git-compat-util.h
+++ b/git-compat-util.h
@@@ -1262,7 -1265,36 +1256,31 @@@ extern int BUG_exit_code
  __attribute__((format (printf, 3, 4))) NORETURN
  void BUG_fl(const char *file, int line, const char *fmt, ...);
  #define BUG(...) BUG_fl(__FILE__, __LINE__, __VA_ARGS__)
 -#else
 -__attribute__((format (printf, 1, 2))) NORETURN
 -void BUG(const char *fmt, ...);
 -#endif
  
+ #ifdef __APPLE__
+ #define FSYNC_METHOD_DEFAULT FSYNC_METHOD_WRITEOUT_ONLY
+ #else
+ #define FSYNC_METHOD_DEFAULT FSYNC_METHOD_FSYNC
+ #endif
+ 
+ enum fsync_action {
+       FSYNC_WRITEOUT_ONLY,
+       FSYNC_HARDWARE_FLUSH
+ };
+ 
+ /*
+  * Issues an fsync against the specified file according to the specified mode.
+  *
+  * FSYNC_WRITEOUT_ONLY attempts to use interfaces available on some operating
+  * systems to flush the OS cache without issuing a flush command to the storage
+  * controller. If those interfaces are unavailable, the function fails with
+  * ENOSYS.
+  *
+  * FSYNC_HARDWARE_FLUSH does an OS writeout and hardware flush to ensure that
+  * changes are durable. It is not expected to fail.
+  */
+ int git_fsync(int fd, enum fsync_action action);
+ 
  /*
   * Preserves errno, prints a message, but gives no warning for ENOENT.
   * Returns 0 on success, which includes trying to unlink an object that does