[Xen-changelog] [xen staging] libvchan: create xenstore entries in one transaction

[p***@xen.org]

commit b72624aad5b00f2f6e976aef4d62eeda83fd0218
Author: Marek Marczykowski-Górecki <***@invisiblethingslab.com>
AuthorDate: Wed Oct 31 00:49:05 2018 +0100
Commit: Wei Liu <***@citrix.com>
CommitDate: Thu Nov 1 10:21:00 2018 +0000

libvchan: create xenstore entries in one transaction

This will prevent race when client waits for server with xs_watch - all
entries should appear at once.

Signed-off-by: Marek Marczykowski-Górecki <***@invisiblethingslab.com>
Acked-by: Wei Liu <***@citrix.com>
---
tools/libvchan/init.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/tools/libvchan/init.c b/tools/libvchan/init.c
index 0b3759a056..ba5a6eb29e 100644
--- a/tools/libvchan/init.c
+++ b/tools/libvchan/init.c
@@ -250,6 +250,7 @@ static int init_xs_srv(struct libxenvchan *ctrl, int domain, const char* xs_base
char buf[64];
char ref[16];
char* domid_str = NULL;
+ xs_transaction_t xs_trans = NULL;
xs = xs_domain_open();
if (!xs)
goto fail;
@@ -265,21 +266,31 @@ static int init_xs_srv(struct libxenvchan *ctrl, int domain, const char* xs_base
perms[1].id = domain;
perms[1].perms = XS_PERM_READ;

+retry_transaction:
+ xs_trans = xs_transaction_start(xs);
+ if (!xs_trans)
+ goto fail_xs_open;
+
snprintf(ref, sizeof ref, "%d", ring_ref);
snprintf(buf, sizeof buf, "%s/ring-ref", xs_base);
- if (!xs_write(xs, 0, buf, ref, strlen(ref)))
+ if (!xs_write(xs, xs_trans, buf, ref, strlen(ref)))
goto fail_xs_open;
- if (!xs_set_permissions(xs, 0, buf, perms, 2))
+ if (!xs_set_permissions(xs, xs_trans, buf, perms, 2))
goto fail_xs_open;

snprintf(ref, sizeof ref, "%d", ctrl->event_port);
snprintf(buf, sizeof buf, "%s/event-channel", xs_base);
- if (!xs_write(xs, 0, buf, ref, strlen(ref)))
+ if (!xs_write(xs, xs_trans, buf, ref, strlen(ref)))
goto fail_xs_open;
- if (!xs_set_permissions(xs, 0, buf, perms, 2))
+ if (!xs_set_permissions(xs, xs_trans, buf, perms, 2))
goto fail_xs_open;

- ret = 0;
+ if (!xs_transaction_end(xs, xs_trans, 0)) {
+ if (errno == EAGAIN)
+ goto retry_transaction;
+ } else {
+ ret = 0;
+ }
fail_xs_open:
free(domid_str);
xs_daemon_close(xs);
--
generated by git-patchbot for /home/xen/git/xen.git#staging