[musl] [PATCH v2] add renameat2 linux syscall wrapper

[Tony Ambardar <tony.ambardar@gmail.com>]

This syscall is available since Linux 3.15 and also implemented in glibc
from version 2.28. It is commonly used in filesystem or security contexts.

Constants RENAME_NOREPLACE, RENAME_EXCHANGE, RENAME_WHITEOUT are guarded by
_GNU_SOURCE as with glibc.

Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
---
v1 -> v2:
 * align related constants
 * drop 'int' from 'unsigned int'
 * add fallback to SYS_renameat where applicable
---
 include/stdio.h       |  7 +++++++
 src/linux/renameat2.c | 12 ++++++++++++
 2 files changed, 19 insertions(+)
 create mode 100644 src/linux/renameat2.c

diff --git a/include/stdio.h b/include/stdio.h
index cb858618..4ea4c170 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -158,6 +158,13 @@ char *ctermid(char *);
 #define L_ctermid 20
 #endif
 
+#if defined(_GNU_SOURCE)
+#define RENAME_NOREPLACE (1 << 0)
+#define RENAME_EXCHANGE  (1 << 1)
+#define RENAME_WHITEOUT  (1 << 2)
+
+int renameat2(int, const char *, int, const char *, unsigned);
+#endif
 
 #if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
  || defined(_BSD_SOURCE)
diff --git a/src/linux/renameat2.c b/src/linux/renameat2.c
new file mode 100644
index 00000000..48ee8d53
--- /dev/null
+++ b/src/linux/renameat2.c
@@ -0,0 +1,12 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include "syscall.h"
+
+int renameat2(int oldfd, const char *old, int newfd, const char *new, unsigned flags)
+{
+	int r = __syscall(SYS_renameat2, oldfd, old, newfd, new, flags);
+#ifdef SYS_renameat
+	if (r==-ENOSYS && !flags) r = __syscall(SYS_renameat, oldfd, old, newfd, new);
+#endif
+	return __syscall_ret(r);
+}
-- 
2.34.1