Re: [Xen-devel] Why xs_domain_open() in fs_backend

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2010-10-13 at 08:19 +0100, Jiang, Yunhong wrote:
> the xenstore_client.c does not use watch feature at all.

I've occasionally thought that it might be useful to have a
xenstore-watch command for skanky scripting purposes so below is a patch
to add one.

I don't know how useful it is generally but it can be used to shows that
"xenstore-watch -s x" (i.e. xs_daemon_open) does appear to be broken.

Subject: xenstore: add xenstore-watch command line client

# xenstore-watch x | while read w ; do
> echo "watch fired on $w"
> echo "value" $(xenstore-read $w)
> echo
> done

# xenstore-write x/y/z 42

output from while loop:
        watch fired on x/t/z
        value 42

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

diff -r 0b69bd41cf15 tools/xenstore/Makefile
--- a/tools/xenstore/Makefile   Wed Oct 13 13:47:32 2010 +0100
+++ b/tools/xenstore/Makefile   Wed Oct 13 13:56:08 2010 +0100
@@ -9,7 +9,7 @@ CFLAGS += $(CFLAGS_libxenctrl)
 CFLAGS += $(CFLAGS_libxenctrl)
 
 CLIENTS := xenstore-exists xenstore-list xenstore-read xenstore-rm 
xenstore-chmod
-CLIENTS += xenstore-write xenstore-ls
+CLIENTS += xenstore-write xenstore-ls xenstore-watch
 
 XENSTORED_OBJS = xenstored_core.o xenstored_watch.o xenstored_domain.o 
xenstored_transaction.o xs_lib.o talloc.o utils.o tdb.o hashtable.o
 
diff -r 0b69bd41cf15 tools/xenstore/xenstore_client.c
--- a/tools/xenstore/xenstore_client.c  Wed Oct 13 13:47:32 2010 +0100
+++ b/tools/xenstore/xenstore_client.c  Wed Oct 13 13:56:08 2010 +0100
@@ -36,6 +36,7 @@ enum mode {
     MODE_read,
     MODE_rm,
     MODE_write,
+    MODE_watch,
 };
 
 static char *output_buf = NULL;
@@ -95,6 +96,9 @@ usage(enum mode mode, int incl_mode, con
     case MODE_chmod:
        mstr = incl_mode ? "chmod " : "";
        errx(1, "Usage: %s %s[-h] [-u] [-r] [-s] key <mode [modes...]>", 
progname, mstr);
+    case MODE_watch:
+       mstr = incl_mode ? "watch " : "";
+       errx(1, "Usage: %s %s[-h] [-n NR] key", progname, mstr);
     }
 }
 
@@ -263,9 +267,28 @@ do_chmod(char *path, struct xs_permissio
     }
 }
 
+static void
+do_watch(struct xs_handle *xsh, int max_events)
+{
+    int count = 0;
+    char **vec = NULL;
+
+    for ( count = 0; max_events == -1 || count < max_events; count++ ) {
+       unsigned int num;
+
+       vec = xs_read_watch(xsh, &num);
+       if (vec == NULL)
+           continue;
+
+       printf("%s\n", vec[XS_WATCH_PATH]);
+       fflush(stdout);
+       free(vec);
+    }
+}
+
 static int
 perform(enum mode mode, int optind, int argc, char **argv, struct xs_handle 
*xsh,
-        xs_transaction_t xth, int prefix, int tidy, int upto, int recurse)
+        xs_transaction_t xth, int prefix, int tidy, int upto, int recurse, int 
nr_watches)
 {
     switch (mode) {
     case MODE_ls:
@@ -428,6 +451,15 @@ perform(enum mode mode, int optind, int 
             do_chmod(path, perms, nperms, upto, recurse, xsh, xth);
             break;
         }
+        case MODE_watch: {
+            for (; argv[optind]; optind++) {
+                const char *w = argv[optind];
+
+                if (!xs_watch(xsh, w, w))
+                    errx(1, "Unable to add watch on %s\n", w);
+            }
+            do_watch(xsh, nr_watches);
+        }
         }
     }
 
@@ -452,6 +484,8 @@ static enum mode lookup_mode(const char 
        return MODE_write;
     else if (strcmp(m, "read") == 0)
        return MODE_read;
+    else if (strcmp(m, "watch") == 0)
+       return MODE_watch;
 
     errx(1, "unknown mode %s\n", m);
     return 0;
@@ -467,6 +501,7 @@ main(int argc, char **argv)
     int tidy = 0;
     int upto = 0;
     int recurse = 0;
+    int nr_watches = -1;
     int transaction;
     struct winsize ws;
     enum mode mode;
@@ -500,10 +535,11 @@ main(int argc, char **argv)
            {"tidy",    0, 0, 't'}, /* MODE_rm */
            {"upto",    0, 0, 'u'}, /* MODE_chmod */
            {"recurse", 0, 0, 'r'}, /* MODE_chmod */
+           {"number",  1, 0, 'n'}, /* MODE_watch */
            {0, 0, 0, 0}
        };
 
-       c = getopt_long(argc - switch_argv, argv + switch_argv, "hfsptur",
+       c = getopt_long(argc - switch_argv, argv + switch_argv, "hfspturn:",
                        long_options, &index);
        if (c == -1)
            break;
@@ -548,6 +584,12 @@ main(int argc, char **argv)
            else
                usage(mode, switch_argv, argv[0]);
            break;
+       case 'n':
+           if ( mode == MODE_watch )
+               nr_watches = atoi(optarg);
+           else
+               usage(mode, switch_argv, argv[0]);
+           break;
        }
     }
 
@@ -575,6 +617,7 @@ main(int argc, char **argv)
        transaction = (argc - switch_argv - optind) > 2;
        break;
     case MODE_ls:
+    case MODE_watch:
        transaction = 0;
        break;
     default:
@@ -601,7 +644,7 @@ again:
            errx(1, "couldn't start transaction");
     }
 
-    ret = perform(mode, optind, argc - switch_argv, argv + switch_argv, xsh, 
xth, prefix, tidy, upto, recurse);
+    ret = perform(mode, optind, argc - switch_argv, argv + switch_argv, xsh, 
xth, prefix, tidy, upto, recurse, nr_watches);
 
     if (transaction && !xs_transaction_end(xsh, xth, ret)) {
        if (ret == 0 && errno == EAGAIN) {



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