Implement file:sendfile

Allow Erlang code to use sendfile() where available by wrapping it as
file:sendfile/4 and file:sendfile/2.

sendfile(2) - Linux man page:
"sendfile() copies data between one file descriptor and another.
Because this copying is done within the kernel, sendfile() is more
efficient than the combination of read(2) and write(2), which would
require transferring data to and from user space."

1 files changed, 44 insertions, 0 deletions

diff --git a/erts/emulator/drivers/unix/unix_efile.c b/erts/emulator/drivers/unix/unix_efile.c
index 4b3934657c..5b001b3819 100644
--- a/erts/emulator/drivers/unix/unix_efile.c
+++ b/erts/emulator/drivers/unix/unix_efile.c
@@ -33,6 +33,9 @@
 #include <sys/types.h>
 #include <sys/uio.h>
 #endif
+#if defined(__linux__) || (defined(__sun) && defined(__SVR4))
+#include <sys/sendfile.h>
+#endif
 
 #if defined(__APPLE__) && defined(__MACH__) && !defined(__DARWIN__)
 #define DARWIN 1
@@ -1464,3 +1467,44 @@ efile_fadvise(Efile_error* errInfo, int fd, Sint64 offset,
     return check_error(0, errInfo);
 #endif
 }
+
+#ifdef HAVE_SENDFILE
+int
+efile_sendfile(Efile_error* errInfo, int in_fd, int out_fd,
+	       off_t *offset, size_t *count)
+{
+#if defined(__linux__) || (defined(__sun) && defined(__SVR4))
+    ssize_t retval = sendfile(out_fd, in_fd, offset, *count);
+    if (retval >= 0) {
+	if (retval != *count) {
+	    *count = retval;
+	    retval = -1;
+	    errno = EAGAIN;
+	} else {
+	    *count = retval;
+	}
+    } else if (retval == -1 && (errno == EINTR || errno == EAGAIN)) {
+	*count = 0;
+    }
+    return check_error(retval == -1 ? -1 : 0, errInfo);
+#elif defined(DARWIN)
+    off_t len = *count;
+    int retval = sendfile(in_fd, out_fd, *offset, &len, NULL, 0);
+    *count = len;
+    return check_error(retval, errInfo);
+#elif defined(__FreeBSD__) || defined(__DragonFly__)
+    off_t len = 0;
+    int retval = sendfile(in_fd, out_fd, *offset, *count, NULL, &len, 0);
+    *count = len;
+    return check_error(retval, errInfo);
+#endif
+}
+#else /* no sendfile() */
+int
+efile_sendfile(Efile_error* errInfo, int in_fd, int out_fd,
+	       off_t *offset, size_t *count)
+{
+    errno = ENOTSUP;
+    return check_error(-1, errInfo);
+}
+#endif