Intercept dup2()

fcntl_helpers.c

 #include <fcntl.h>
 #include <unistd.h>
+#include <errno.h>
 
 /* Since open() and close() are re-defined in nocache.c, it's not
  * possible to include <fcntl.h> there. So we do it here. */
@@ -14,6 +15,12 @@ int fadv_noreuse(int fd, off_t offset, off_t len)
         return posix_fadvise(fd, offset, len, POSIX_FADV_NOREUSE);
 }
 
+int valid_fd(int fd)
+{
+    /* will return 1 if fd is opened */
+    return fcntl(fd, F_GETFL) != -1 || errno != EBADF;
+}
+
 void sync_if_writable(int fd)
 {
     int r;

nocache.c

@@ -13,6 +13,7 @@ int (*_original_open)(const char *pathname, int flags, mode_t mode);
 int (*_original_creat)(const char *pathname, int flags, mode_t mode);
 int (*_original_openat)(int dirfd, const char *pathname, int flags, mode_t mode);
 int (*_original_dup)(int fd);
+int (*_original_dup2)(int newfd, int oldfd);
 int (*_original_close)(int fd);
 
 static void init(void) __attribute__((constructor));
@@ -31,6 +32,7 @@ int openat64(int dirfd, const char *pathname, int flags, mode_t mode)
 int __openat_2(int dirfd, const char *pathname, int flags, mode_t mode)
     __attribute__ ((alias ("openat")));
 int dup(int oldfd);
+int dup2(int oldfd, int newfd);
 int close(int fd);
 
 static void store_pageinfo(int fd);
@@ -38,6 +40,7 @@ static void free_unclaimed_pages(int fd);
 
 extern int fadv_dontneed(int fd, off_t offset, off_t len);
 extern int fadv_noreuse(int fd, off_t offset, off_t len);
+extern int valid_fd(int fd);
 extern void sync_if_writable(int fd);
 
 #define _MAX_FDS 1024
@@ -62,6 +65,7 @@ static void init(void)
     _original_openat = (int (*)(int, const char *, int, mode_t))
         dlsym(RTLD_NEXT, "openat");
     _original_dup = (int (*)(int)) dlsym(RTLD_NEXT, "dup");
+    _original_dup2 = (int (*)(int, int)) dlsym(RTLD_NEXT, "dup2");
     _original_close = (int (*)(int)) dlsym(RTLD_NEXT, "close");
     PAGESIZE = getpagesize();
     for(i = 0; i < _MAX_FDS; i++)
@@ -127,6 +131,22 @@ int dup(int oldfd)
     return fd;
 }
 
+int dup2(int oldfd, int newfd)
+{
+    int ret;
+
+    /* if newfd is already opened, the kernel will close it directly
+     * once dup2 is invoked. So now is the last chance to mark the
+     * pages as "DONTNEED" */
+    if(valid_fd(newfd))
+        free_unclaimed_pages(newfd);
+
+    if((ret = _original_dup2(oldfd, newfd)) != -1) {
+        store_pageinfo(newfd);
+    }
+    return ret;
+}
+
 int close(int fd)
 {
     free_unclaimed_pages(fd);