[Spice-devel] [PATCH 2/3 v3] replay: allows to specify a filter for record output

[Frediano Ziglio]

This allows compression using external programs or any type
of filters.

To use it set SPICE_WORKER_RECORD_FILTER environment to the
filter command you want to use. The command is executed with
g_spawn_async_with_pipes (which uses execve) so is not a shell
command although the command is parsed using g_shell_parse_argv
which split arguments as shell does.

One easy way to use it is to just use a compressor like gzip with

  export SPICE_WORKER_RECORD_FILENAME=/tmp/qemu_record.gz
  export SPICE_WORKER_RECORD_FILTER=gzip
  qemu ...

The filter will receive the recording on standard input and is
supposed to write in output filename (which is the standard output).
You can use additional arguments in SPICE_WORKER_RECORD_FILTER to
specify for instance compression level.

Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
---
 server/red-record-qxl.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

Changes from v2:
- clarify comment removed unneeded and confusing notes;
- rename out_setup to child_output_setup;
- add some comments.

diff --git a/server/red-record-qxl.c b/server/red-record-qxl.c
index 5337699..c6cd963 100644
--- a/server/red-record-qxl.c
+++ b/server/red-record-qxl.c
@@ -21,6 +21,8 @@
 
 #include <stdbool.h>
 #include <inttypes.h>
+#include <fcntl.h>
+#include <glib.h>
 #include "red-worker.h"
 #include "red-common.h"
 #include "memslot.h"
@@ -834,10 +836,26 @@ void red_record_qxl_command(RedRecord *record, RedMemSlotInfo *slots,
     }
 }
 
+/**
+ * Redirects child output to the file specified
+ */
+static void child_output_setup(gpointer user_data)
+{
+    int fd = GPOINTER_TO_INT(user_data);
+
+    while (dup2(fd, STDOUT_FILENO) < 0 && errno == EINTR)
+        continue;
+    close(fd);
+
+    // make sure file is not closed calling exec()
+    fcntl(STDOUT_FILENO, F_SETFD, 0);
+}
+
 RedRecord *red_record_new(const char *filename)
 {
     static const char header[] = "SPICE_REPLAY 1\n";
 
+    const char *filter;
     FILE *f;
     RedRecord *record;
 
@@ -846,6 +864,33 @@ RedRecord *red_record_new(const char *filename)
         spice_error("failed to open recording file %s\n", filename);
     }
 
+    filter = getenv("SPICE_WORKER_RECORD_FILTER");
+    if (filter) {
+        gint argc;
+        gchar **argv = NULL;
+        GError *error = NULL;
+        GPid child_pid;
+        gboolean ret;
+        gint fd_in;
+
+        ret = g_shell_parse_argv(filter, &argc, &argv, &error);
+
+        if (ret)
+            ret = g_spawn_async_with_pipes(NULL, argv, NULL, G_SPAWN_SEARCH_PATH,
+                               child_output_setup, GINT_TO_POINTER(fileno(f)), &child_pid,
+                               &fd_in, NULL, NULL, &error);
+
+        g_strfreev(argv);
+        if (!ret) {
+            g_error_free(error);
+            fclose(f);
+            spice_error("failed to setup filter for replay");
+        }
+        while (dup2(fd_in, fileno(f)) < 0 && errno == EINTR)
+            continue;
+        close(fd_in);
+    }
+
     if (fwrite(header, sizeof(header)-1, 1, f) != 1) {
         spice_error("failed to write replay header");
     }
-- 
2.7.4