[Xen-devel] [RFC PATCH 4/8] libxl: wait up to 5s in libxl_console_exec for xenconsoled

[Wei Liu <wei.liu2@xxxxxxxxxx>]

Wait until the tty node is available before exec'ing xenconsole.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/libxl/libxl.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 0bc805e..a611b29 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -1780,10 +1780,14 @@ int libxl_console_exec(libxl_ctx *ctx, uint32_t domid, 
int cons_num,
                        libxl_console_type type)
 {
     GC_INIT(ctx);
+    int rc;
     char *p = GCSPRINTF("%s/xenconsole", libxl__private_bindir_path());
     char *domid_s = GCSPRINTF("%d", domid);
     char *cons_num_s = GCSPRINTF("%d", cons_num);
     char *cons_type_s;
+    char *tty_path;
+    const char *tty;
+    int retry = 50;             /* wait for 50 * 0.1 = 5 s for xenconsoled */
 
     switch (type) {
     case LIBXL_CONSOLE_TYPE_PV:
@@ -1793,6 +1797,28 @@ int libxl_console_exec(libxl_ctx *ctx, uint32_t domid, 
int cons_num,
         cons_type_s = "serial";
         break;
     default:
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    /* Make sure tty shows up before exec'ing xenconsole client */
+    rc = libxl__console_tty_path(gc, domid, cons_num, type, &tty_path);
+    if (rc) goto out;
+
+    while (retry-- > 0) {
+        rc = libxl__xs_read_checked(gc, XBT_NULL, tty_path, &tty);
+        if (rc) goto out;
+
+        if (tty != NULL && tty[0] != '\0')
+            break;
+
+        LOG(DEBUG, "TTY is not yet ready, retry");
+        usleep(100000);
+    }
+
+    if (retry == 0 && (!tty || tty[0] == '\0')) {
+        LOG(ERROR, "Failed to get tty from xenstore\n");
+        rc = ERROR_FAIL;
         goto out;
     }
 
@@ -1800,7 +1826,7 @@ int libxl_console_exec(libxl_ctx *ctx, uint32_t domid, 
int cons_num,
 
 out:
     GC_FREE;
-    return ERROR_FAIL;
+    return rc;
 }
 
 int libxl_console_get_tty(libxl_ctx *ctx, uint32_t domid, int cons_num,
-- 
2.1.4


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