[Qemu-devel] [PATCH 08/17] migration-local: override save_page for page transmit

[Lei Li <lilei@linux.vnet.ibm.com>]

This patch implements save_page callback for the outside
of page flipping. It will write the address of the page
on the Unix socket and flip the page data on pipe by
vmsplice(). Every page address would have a header flag
RAM_SAVE_FLAG_HOOK, which will trigger the load hook to
receive it in incoming side as well.

Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
---
 migration-local.c |   63 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 63 insertions(+), 0 deletions(-)

diff --git a/migration-local.c b/migration-local.c
index f479530..9453ec8 100644
--- a/migration-local.c
+++ b/migration-local.c
@@ -116,6 +116,68 @@ static int qemu_local_close(void *opaque)
     return 0;
 }
 
+static int send_pipefd(int sockfd, int pipefd);
+
+static size_t qemu_local_save_ram(QEMUFile *f, void *opaque,
+                                  MemoryRegion *mr, ram_addr_t offset,
+                                  size_t size, int *bytes_sent)
+{
+    QEMUFileLocal *s = opaque;
+    ram_addr_t current_addr = mr->ram_addr + offset;
+    void *ram_addr;
+    ssize_t ret;
+
+    if (s->unix_page_flipping) {
+        qemu_put_be64(s->file, current_addr | RAM_SAVE_FLAG_HOOK);
+        qemu_fflush(s->file);
+
+        if (!s->pipefd_passed) {
+            ret = send_pipefd(s->sockfd, s->pipefd[0]);
+            if (ret < 0) {
+                fprintf(stderr, "failed to pass PIPE\n");
+                return ret;
+            }
+            s->pipefd_passed = true;
+        }
+
+        ram_addr = memory_region_get_ram_ptr(mr) + offset;
+
+        /* vmsplice page data to pipe */
+        struct iovec iov = {
+            .iov_base = ram_addr,
+            .iov_len  = size,
+        };
+
+        /*
+         * The flag SPLICE_F_MOVE is introduced in kernel for the page
+         * flipping feature in QEMU, which will move pages rather than
+         * copying, previously unused.
+         *
+         * If a move is not possible the kernel will transparently fall
+         * back to copying data.
+         *
+         * For older kernels the SPLICE_F_MOVE would be ignored and a copy
+         * would occur.
+         */
+
+        ret = vmsplice(s->pipefd[1], &iov, 1, SPLICE_F_GIFT | SPLICE_F_MOVE);
+        if (ret == -1) {
+            if (errno != EAGAIN && errno != EINTR) {
+                fprintf(stderr, "vmsplice save error: %s\n", strerror(errno));
+                return ret;
+            }
+        } else {
+            if (bytes_sent) {
+                *bytes_sent = size;
+            }
+            DPRINTF("block_offset: %lu, offset: %lu\n", mr->ram_addr, offset);
+            return 0;
+        }
+    }
+
+    return RAM_SAVE_CONTROL_NOT_SUPP;
+}
+
 static const QEMUFileOps pipe_read_ops = {
     .get_fd        = qemu_local_get_sockfd,
     .get_buffer    = qemu_local_get_buffer,
@@ -126,6 +188,7 @@ static const QEMUFileOps pipe_write_ops = {
     .get_fd             = qemu_local_get_sockfd,
     .writev_buffer      = qemu_local_writev_buffer,
     .close              = qemu_local_close,
+    .save_page          = qemu_local_save_ram
 };
 
 QEMUFile *qemu_fopen_socket_local(int sockfd, const char *mode)
-- 
1.7.7.6