renameat2
Ken Brown
kbrown@cornell.edu
Fri Aug 18 15:16:00 GMT 2017
Linux has a system call 'renameat2' which is like renameat but has an extra 'flags' argument. In particular, one can pass the RENAME_NOREPLACE flag to cause the rename to fail with EEXIST if the target of the rename exists. See
http://man7.org/linux/man-pages/man2/rename.2.html
macOS has a similar functionality, provided by the function 'renameatx_np' with the flag RENAME_EXCL.
There's also a recently introduced Gnulib module 'renameat2', but it requires two system calls on Cygwin (one to test existence and the second to do the rename), so that there is a race condition. On Linux and macOS it uses renameat2 and renameatx_np to avoid the race.
The attached patch implements renameat2 on Cygwin (but only supporting the RENAME_NOREPLACE flag). I've written it so that a rename that just changes case on a case-insensitive file system succeeds.
If the patch is accepted, I'll submit a second patch that documents the new function.
Here's a simple test program:
$ cat rename_noreplace.c
#include <fcntl.h>
#include <stdio.h>
#include <cygwin/fs.h>
int
main ()
{
int res = renameat2 (AT_FDCWD, "foo", AT_FDCWD, "bar", RENAME_NOREPLACE);
if (res < 0)
perror ("renameat2");
}
$ gcc -o rename_noreplace rename_noreplace.c
$ touch foo bar
$ ./rename_noreplace.exe
renameat2: File exists
$ ls foo bar
bar foo
$ rm bar
$ ./rename_noreplace.exe
$ ls foo bar
ls: cannot access 'foo': No such file or directory
bar
Ken
-------------- next part --------------
From 23edb25c9c0b6a21aefb10372db945807b2b8e3f Mon Sep 17 00:00:00 2001
From: Ken Brown <kbrown@cornell.edu>
Date: Thu, 17 Aug 2017 09:12:15 -0400
Subject: [PATCH] cygwin: Implement renameat2
Define the RENAME_* flags in <cygwin/fs.h> as defined on Linux in
<linux/fs.h>, but support only RENAME_NOREPLACE.
---
newlib/libc/include/stdio.h | 3 +++
winsup/cygwin/common.din | 1 +
winsup/cygwin/include/cygwin/fs.h | 5 +++++
winsup/cygwin/include/cygwin/version.h | 4 +++-
winsup/cygwin/syscalls.cc | 41 +++++++++++++++++++++++++++++-----
5 files changed, 48 insertions(+), 6 deletions(-)
diff --git a/newlib/libc/include/stdio.h b/newlib/libc/include/stdio.h
index 5d8cb1092..331a1cf07 100644
--- a/newlib/libc/include/stdio.h
+++ b/newlib/libc/include/stdio.h
@@ -384,6 +384,9 @@ int _EXFUN(vdprintf, (int, const char *__restrict, __VALIST)
#endif
#if __ATFILE_VISIBLE
int _EXFUN(renameat, (int, const char *, int, const char *));
+# ifdef __CYGWIN__
+int _EXFUN(renameat2, (int, const char *, int, const char *, unsigned int));
+# endif
#endif
/*
diff --git a/winsup/cygwin/common.din b/winsup/cygwin/common.din
index 8da432b8a..ca6ff3cf9 100644
--- a/winsup/cygwin/common.din
+++ b/winsup/cygwin/common.din
@@ -1168,6 +1168,7 @@ remquof NOSIGFE
remquol NOSIGFE
rename SIGFE
renameat SIGFE
+renameat2 SIGFE
res_close = __res_close SIGFE
res_init = __res_init SIGFE
res_mkquery = __res_mkquery SIGFE
diff --git a/winsup/cygwin/include/cygwin/fs.h b/winsup/cygwin/include/cygwin/fs.h
index f606ffc39..14454376f 100644
--- a/winsup/cygwin/include/cygwin/fs.h
+++ b/winsup/cygwin/include/cygwin/fs.h
@@ -19,4 +19,9 @@ details. */
#define BLKPBSZGET 0x0000127b
#define BLKGETSIZE64 0x00041268
+/* Flags for renameat2, from /usr/include/linux/fs.h. */
+#define RENAME_NOREPLACE (1 << 0)
+#define RENAME_EXCHANGE (1 << 1)
+#define RENAME_WHITEOUT (1 << 2)
+
#endif
diff --git a/winsup/cygwin/include/cygwin/version.h b/winsup/cygwin/include/cygwin/version.h
index efd4ac017..7640abfad 100644
--- a/winsup/cygwin/include/cygwin/version.h
+++ b/winsup/cygwin/include/cygwin/version.h
@@ -481,12 +481,14 @@ details. */
314: Export explicit_bzero.
315: Export pthread_mutex_timedlock.
316: Export pthread_rwlock_timedrdlock, pthread_rwlock_timedwrlock.
+ 317: Export renameat2. Add RENAME_NOREPLACE, RENAME_EXCHANGE,
+ RENAME_WHITEOUT.
Note that we forgot to bump the api for ualarm, strtoll, strtoull,
sigaltstack, sethostname. */
#define CYGWIN_VERSION_API_MAJOR 0
-#define CYGWIN_VERSION_API_MINOR 316
+#define CYGWIN_VERSION_API_MINOR 317
/* There is also a compatibity version number associated with the shared memory
regions. It is incremented when incompatible changes are made to the shared
diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
index 885931632..d756f5f35 100644
--- a/winsup/cygwin/syscalls.cc
+++ b/winsup/cygwin/syscalls.cc
@@ -60,6 +60,7 @@ details. */
#include "tls_pbuf.h"
#include "sync.h"
#include "child_info.h"
+#include <cygwin/fs.h> /* needed for RENAME_NOREPLACE */
#undef _close
#undef _lseek
@@ -2048,8 +2049,12 @@ nt_path_has_executable_suffix (PUNICODE_STRING upath)
return false;
}
-extern "C" int
-rename (const char *oldpath, const char *newpath)
+/* If newpath names an existing file and the RENAME_NOREPLACE flag is
+ specified, fail with EEXIST. Exception: Don't fail if the purpose
+ of the rename is just to change the case of oldpath on a
+ case-insensitive file system. */
+static int
+rename2 (const char *oldpath, const char *newpath, unsigned int flags)
{
tmp_pathbuf tp;
int res = -1;
@@ -2068,6 +2073,12 @@ rename (const char *oldpath, const char *newpath)
__try
{
+ if (flags & ~RENAME_NOREPLACE)
+ /* RENAME_NOREPLACE is the only flag currently supported. */
+ {
+ set_errno (ENOTSUP);
+ __leave;
+ }
if (!*oldpath || !*newpath)
{
/* Reject rename("","x"), rename("x",""). */
@@ -2337,6 +2348,13 @@ rename (const char *oldpath, const char *newpath)
__leave;
}
+ /* Should we replace an existing file? */
+ if ((removepc || dstpc->exists ()) && (flags & RENAME_NOREPLACE))
+ {
+ set_errno (EEXIST);
+ __leave;
+ }
+
/* Opening the file must be part of the transaction. It's not sufficient
to call only NtSetInformationFile under the transaction. Therefore we
have to start the transaction here, if necessary. */
@@ -2578,6 +2596,12 @@ rename (const char *oldpath, const char *newpath)
return res;
}
+extern "C" int
+rename (const char *oldpath, const char *newpath)
+{
+ return rename2 (oldpath, newpath, 0);
+}
+
extern "C" int
system (const char *cmdstring)
{
@@ -4719,8 +4743,8 @@ readlinkat (int dirfd, const char *__restrict pathname, char *__restrict buf,
}
extern "C" int
-renameat (int olddirfd, const char *oldpathname,
- int newdirfd, const char *newpathname)
+renameat2 (int olddirfd, const char *oldpathname,
+ int newdirfd, const char *newpathname, unsigned int flags)
{
tmp_pathbuf tp;
__try
@@ -4731,13 +4755,20 @@ renameat (int olddirfd, const char *oldpathname,
char *newpath = tp.c_get ();
if (gen_full_path_at (newpath, newdirfd, newpathname))
__leave;
- return rename (oldpath, newpath);
+ return rename2 (oldpath, newpath, flags);
}
__except (EFAULT) {}
__endtry
return -1;
}
+extern "C" int
+renameat (int olddirfd, const char *oldpathname,
+ int newdirfd, const char *newpathname)
+{
+ return renameat2 (olddirfd, oldpathname, newdirfd, newpathname, 0);
+}
+
extern "C" int
scandirat (int dirfd, const char *pathname, struct dirent ***namelist,
int (*select) (const struct dirent *),
--
2.14.1
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