win32: partial implementation of sync(2)

Provide a partial implementation of sync(2), so sync(1) can actually
do something in some circumstances:

- Only logical drives are handled.

- Flushing buffers requires administrative privileges.  If run as
  a normal user nothing will happen.

2 files changed, 25 insertions, 1 deletions

diff --git a/include/mingw.h b/include/mingw.h
index 49e792b69..c4849215b 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -471,7 +471,6 @@ NOIMPL(setuid,uid_t gid UNUSED_PARAM);
 NOIMPL(seteuid,uid_t gid UNUSED_PARAM);
 unsigned int sleep(unsigned int seconds);
 int symlink(const char *target, const char *linkpath);
-static inline void sync(void) { sleep(2); }
 long sysconf(int name);
 IMPL(getpagesize,int,4096,void);
 NOIMPL(ttyname_r,int fd UNUSED_PARAM, char *buf UNUSED_PARAM, int sz UNUSED_PARAM);
@@ -479,6 +478,7 @@ int mingw_unlink(const char *pathname);
 pid_t vfork(void);
 int mingw_access(const char *name, int mode);
 int mingw_rmdir(const char *name);
+void mingw_sync(void);
 int mingw_isatty(int fd);
 
 #define dup2 mingw_dup2
@@ -488,6 +488,7 @@ int mingw_isatty(int fd);
 #define close mingw_close
 #define unlink mingw_unlink
 #define rmdir mingw_rmdir
+#define sync mingw_sync
 #undef lseek
 #define lseek mingw_lseek
 
diff --git a/win32/mingw.c b/win32/mingw.c
index 3183cd78e..a65a0a6d1 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1666,6 +1666,29 @@ int mingw_rmdir(const char *path)
         return rmdir(path);
 }
 
+void mingw_sync(void)
+{
+        HANDLE h;
+        FILE *mnt;
+        struct mntent *entry;
+        char name[] = "\\\\.\\C:";
+
+        mnt = setmntent(bb_path_mtab_file, "r");
+        if (mnt) {
+                while ((entry=getmntent(mnt)) != NULL) {
+                        name[4] = entry->mnt_dir[0];
+                        h = CreateFile(name, GENERIC_READ | GENERIC_WRITE,
+                                                FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
+                                                OPEN_EXISTING, 0, NULL);
+                        if (h != INVALID_HANDLE_VALUE) {
+                                FlushFileBuffers(h);
+                                CloseHandle(h);
+                        }
+                }
+                endmntent(mnt);
+        }
+}
+
 #define NUMEXT 5
 static const char win_suffix[NUMEXT][4] = { "sh", "com", "exe", "bat", "cmd" };