Use posix_fadvise when uploading or downloading files.

But ignore it if the call fails, since the file descriptor could be a
non-file (eg. /dev/stdout).

2 files changed, 18 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index bfa6e5d6..3f7123be 100644
--- a/configure.ac
+++ b/configure.ac
@@ -212,6 +212,7 @@ AC_CHECK_FUNCS([\
         ntohl \
         ntohs \
         posix_fallocate \
+        posix_fadvise \
         realpath \
         removexattr \
         setitimer \
diff --git a/src/proto.c b/src/proto.c
index bf3feaed..16cff4fc 100644
--- a/src/proto.c
+++ b/src/proto.c
@@ -872,6 +872,19 @@ guestfs___send (guestfs_h *g, int proc_nr,
   return -1;
 }
 
+static void
+fadvise_sequential (int fd)
+{
+#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_SEQUENTIAL)
+  /* Since the fd might be a non-file, eg. /dev/stdout, just ignore
+   * this when it fails.  It's not clear from the man page, but the
+   * 'advice' parameter is NOT a bitmask.  You can only pass one
+   * parameter with each call.
+   */
+  ignore_value (posix_fadvise (fd, 0, 0, POSIX_FADV_SEQUENTIAL));
+#endif
+}
+
 static int send_file_chunk (guestfs_h *g, int cancel, const char *buf, size_t len);
 static int send_file_data (guestfs_h *g, const char *buf, size_t len);
 static int send_file_cancellation (guestfs_h *g);
@@ -898,6 +911,8 @@ guestfs___send_file (guestfs_h *g, const char *filename)
     return -1;
   }
 
+  fadvise_sequential (fd);
+
   /* Send file in chunked encoding. */
   while (!g->user_cancel) {
     r = read (fd, buf, sizeof buf);
@@ -1131,6 +1146,8 @@ guestfs___recv_file (guestfs_h *g, const char *filename)
     goto cancel;
   }
 
+  fadvise_sequential (fd);
+
   /* Receive the file in chunked encoding. */
   while ((r = receive_file_data (g, &buf)) > 0) {
     if (xwrite (fd, buf, r) == -1) {