libxl: log bootloader output

This involves adding a new log feature to libxl__datacopier, and then
using it.

If the bootloader exits nonzero we print the log filename in a log
message from libxl.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

tools/libxl/libxl_aoutils.c

@@ -118,6 +118,16 @@ static void datacopier_readable(libxl__egc *egc, libxl__ev_fd *ev,
             libxl__ev_fd_deregister(gc, &dc->toread);
             break;
         }
+        if (dc->log) {
+            int wrote = fwrite(buf->buf + buf->used, 1, r, dc->log);
+            if (wrote != r) {
+                assert(ferror(dc->log));
+                assert(errno);
+                LOGE(ERROR, "error logging %s", dc->copywhat);
+                datacopier_callback(egc, dc, 0, errno);
+                return;
+            }
+        }
         buf->used += r;
         dc->used += r;
         assert(buf->used <= sizeof(buf->buf));

tools/libxl/libxl_bootloader.c

@@ -236,6 +236,10 @@ static void bootloader_cleanup(libxl__egc *egc, libxl__bootloader_state *bl)
         libxl__carefd_close(bl->ptys[i].master);
         libxl__carefd_close(bl->ptys[i].slave);
     }
+    if (bl->display.log) {
+        fclose(bl->display.log);
+        bl->display.log = NULL;
+    }
 }
 
 static void bootloader_setpaths(libxl__gc *gc, libxl__bootloader_state *bl)
@@ -258,6 +262,8 @@ void libxl__bootloader_run(libxl__egc *egc, libxl__bootloader_state *bl)
 {
     STATE_AO_GC(bl->ao);
     libxl_domain_build_info *info = bl->info;
+    uint32_t domid = bl->domid;
+    char *logfile_tmp = NULL;
     int rc, r;
 
     libxl__bootloader_init(bl);
@@ -269,6 +275,22 @@ void libxl__bootloader_run(libxl__egc *egc, libxl__bootloader_state *bl)
 
     bootloader_setpaths(gc, bl);
 
+    const char *logfile_leaf = GCSPRINTF("bootloader.%"PRIu32, domid);
+    rc = libxl_create_logfile(CTX, logfile_leaf, &logfile_tmp);
+    if (rc) goto out;
+
+    /* Transfer ownership of log filename to bl and the gc */
+    bl->logfile = logfile_tmp;
+    libxl__ptr_add(gc, logfile_tmp);
+    logfile_tmp = NULL;
+
+    bl->display.log = fopen(bl->logfile, "a");
+    if (!bl->display.log) {
+        LOGE(ERROR, "failed to create bootloader logfile %s", bl->logfile);
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
     for (;;) {
         r = mkdir(bl->outputdir, 0600);
         if (!r) break;
@@ -308,6 +330,7 @@ void libxl__bootloader_run(libxl__egc *egc, libxl__bootloader_state *bl)
  out:
     assert(rc);
  out_ok:
+    free(logfile_tmp);
     bootloader_callback(egc, bl, rc);
 }
 
@@ -465,6 +488,7 @@ static void bootloader_finished(libxl__egc *egc, libxl__ev_child *child,
     libxl__datacopier_kill(&bl->display);
 
     if (status) {
+        LOG(ERROR, "bootloader failed - consult logfile %s", bl->logfile);
         libxl_report_child_exitstatus(CTX, XTL_ERROR, "bootloader",
                                       pid, status);
         rc = ERROR_FAIL;

tools/libxl/libxl_internal.h

@@ -1503,6 +1503,7 @@ struct libxl__datacopier_state {
     int readfd, writefd;
     ssize_t maxsz;
     const char *copywhat, *readwhat, *writewhat; /* for error msgs */
+    FILE *log; /* gets a copy of everything */
     libxl__datacopier_callback *callback;
     /* remaining fields are private to datacopier */
     libxl__ev_fd toread, towrite;
@@ -1565,7 +1566,7 @@ struct libxl__bootloader_state {
     libxl_device_disk *disk;
     uint32_t domid;
     /* private to libxl__run_bootloader */
-    char *outputpath, *outputdir;
+    char *outputpath, *outputdir, *logfile;
     char *diskpath; /* not from gc, represents actually attached disk */
     libxl__openpty_state openpty;
     libxl__openpty_result ptys[2];  /* [0] is for bootloader */