Re: [Xen-devel] [PATCH 1/2] tools/xenstore: Do not abort xenstore-ls if a node disappears while iterating

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

On Fri, 2020-03-20 at 14:12 +0000, Ian Jackson wrote:
> Jürgen Groß writes ("Re: [Xen-devel] [PATCH 1/2] tools/xenstore: Do not abort 
> xenstore-ls if a node disappears while iterating"):
> > No, you just don't care for the transaction to succeed or fail (IMO it
> > should never fail as you are reading only).
> > 
> > So just wrap everything into a transaction.
> 
> Yes.  xenstored will do the needed buffering.
> 
> I think in principle there is a risk here that the transaction might
> run for a long time, if the output from xenstore-ls goes to something
> that blocks (eg a pager) and can't be written all at once.
> 
> But if this is a problem it is a problem afflicting xenstored, not
> xenstore-ls.
> 
> Ian.


So if I do this...

--- a/tools/xenstore/xenstore_client.c
+++ b/tools/xenstore/xenstore_client.c
@@ -658,7 +658,6 @@ main(int argc, char **argv)
     case MODE_write:
        transaction = (argc - switch_argv - optind) > 2;
        break;
-    case MODE_ls:
     case MODE_watch:
        transaction = 0;
        break;
@@ -683,6 +682,7 @@ again:
        xth = xs_transaction_start(xsh);
        if (xth == XBT_NULL)
            errx(1, "couldn't start transaction");
+        printf("started transaction\n");
     }
 
     ret = perform(mode, optind, argc - switch_argv, argv + switch_argv, xsh, 
xth, prefix, tidy, upto, recurse, nr_watches, raw);


... and then repeat my test case as shown in [PATCH 1/1], I should no
longer see...

xenstore-ls: 
could not access permissions for 407: No such file or directory
xenstore-ls: in xs_directory (/local/domain/2/foo/407): No such file or 
directory
0


But it does still happen. And even if I turn the errx() into a warn()
to stop it aborting, and add a warn() when the xs_transaction_end()
returns EAGAIN... that isn't happening either. I'm just getting
inconsistent data, within a transaction.

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