add O_PATH/O_SEARCH support to fcntl.h

I'm not 100% sure that Linux's O_PATH meets the POSIX requirements for
O_SEARCH, but it seems very close if not perfect. and old kernels
ignore it, so O_SEARCH will still work as desired as long as the
caller has read permissions to the directory.

arch/arm/bits/fcntl.h

@@ -10,12 +10,14 @@
 #define O_DIRECTORY  040000
 #define O_NOFOLLOW  0100000
 #define O_CLOEXEC  02000000
+#define O_SEARCH  010000000
 
 #define O_ASYNC      020000
 #define O_DIRECT    0200000
 #define O_LARGEFILE 0400000
 #define O_NOATIME  01000000
 #define O_NDELAY O_NONBLOCK
+#define O_PATH    010000000
 
 #define F_DUPFD  0
 #define F_GETFD  1

arch/i386/bits/fcntl.h

@@ -10,12 +10,14 @@
 #define O_DIRECTORY 0200000
 #define O_NOFOLLOW  0400000
 #define O_CLOEXEC  02000000
+#define O_SEARCH  010000000
 
 #define O_ASYNC      020000
 #define O_DIRECT     040000
 #define O_LARGEFILE 0100000
 #define O_NOATIME  01000000
 #define O_NDELAY O_NONBLOCK
+#define O_PATH    010000000
 
 #define F_DUPFD  0
 #define F_GETFD  1

arch/mips/bits/fcntl.h

@@ -14,6 +14,8 @@
 #define O_NOFOLLOW  0400000
 #define O_NOATIME  01000000
 #define O_CLOEXEC  02000000
+#define O_PATH    010000000
+#define O_SEARCH  010000000
 
 #define O_NDELAY O_NONBLOCK
 

arch/x86_64/bits/fcntl.h

@@ -10,12 +10,14 @@
 #define O_DIRECTORY 0200000
 #define O_NOFOLLOW  0400000
 #define O_CLOEXEC  02000000
+#define O_SEARCH  010000000
 
 #define O_ASYNC      020000
 #define O_DIRECT     040000
 #define O_LARGEFILE       0
 #define O_NOATIME  01000000
 #define O_NDELAY O_NONBLOCK
+#define O_PATH    010000000
 
 #define F_DUPFD  0
 #define F_GETFD  1

include/fcntl.h

@@ -37,7 +37,7 @@ int openat(int, const char *, int, ...);
 int posix_fadvise(int, off_t, off_t, int);
 int posix_fallocate(int, off_t, off_t);
 
-#define O_ACCMODE 03
+#define O_ACCMODE (O_RDWR|O_SEARCH)
 #define O_RDONLY  00
 #define O_WRONLY  01
 #define O_RDWR    02