Today the file descriptor for the access of the event channel driver
is being closed in case of exec(2). For the support of live update of
a daemon using libxenevtchn this can be problematic, so add a way to
keep that file descriptor open.
Add support of a flag XENEVTCHN_NO_CLOEXEC for xenevtchn_open() which
will result in _not_ setting O_CLOEXEC when opening the event channel
driver node.
The caller can then obtain the file descriptor via xenevtchn_fd().
Add an alternative open function xenevtchn_fdopen() which takes that
file descriptor as an additional parameter. This allows to allocate a
xenevtchn_handle and to associate it with that file descriptor.
Signed-off-by: Juergen Gross <jgr...@suse.com>
Reviewed-by: Wei Liu <w...@xen.org>
Reviewed-by: Julien Grall <jgr...@amazon.com>
---
V7:
- new patch
V8:
- some minor comments by Julien Grall addressed
V11:
- rename to xenevtchn_fdopen() (Andrew Cooper)
V12:
- better comments in header file (Andrew Cooper)
- reject flags != 0 if fdopen (Andrew Cooper)
- style (Andrew Cooper)
---
tools/include/xenevtchn.h | 50 +++++++++++++++---------
tools/libs/evtchn/Makefile | 2 +-
tools/libs/evtchn/core.c | 62 ++++++++++++++++++++++--------
tools/libs/evtchn/freebsd.c | 7 +++-
tools/libs/evtchn/libxenevtchn.map | 4 ++
tools/libs/evtchn/linux.c | 6 ++-
tools/libs/evtchn/minios.c | 4 ++
7 files changed, 97 insertions(+), 38 deletions(-)
diff --git a/tools/include/xenevtchn.h b/tools/include/xenevtchn.h
index 3e9b6e7323..10dbe1a06e 100644
--- a/tools/include/xenevtchn.h
+++ b/tools/include/xenevtchn.h
@@ -42,35 +42,47 @@ struct xentoollog_logger;
*/
/*
- * Return a handle to the event channel driver, or NULL on failure, in
- * which case errno will be set appropriately.
+ * Opens the evtchn device node. Return a handle to the event channel
+ * driver, or NULL on failure, in which case errno will be set
+ * appropriately.
*
- * Note: After fork(2) a child process must not use any opened evtchn
- * handle inherited from their parent, nor access any grant mapped
- * areas associated with that handle.
+ * On fork(2):
*
- * The child must open a new handle if they want to interact with
- * evtchn.
+ * After fork, a child process must not use any opened evtchn handle
+ * inherited from their parent. This includes operations such as
+ * poll() on the underlying file descriptor. Calling xenevtchn_close()
+ * is the only safe operation on a xenevtchn_handle which has been
+ * inherited.
*
- * Calling exec(2) in a child will safely (and reliably) reclaim any
- * allocated resources via a xenevtchn_handle in the parent.
+ * The child must open a new handle if they want to interact with
+ * evtchn.
*
- * A child which does not call exec(2) may safely call
- * xenevtchn_close() on a xenevtchn_handle inherited from their
- * parent. This will attempt to reclaim any resources associated with
- * that handle. Note that in some implementations this reclamation may
- * not be completely effective, in this case any affected resources
- * remain allocated.
+ * On exec(2):
*
- * Calling xenevtchn_close() is the only safe operation on a
- * xenevtchn_handle which has been inherited.
+ * Wherever possible, the device node will be opened with O_CLOEXEC,
+ * so it is not inherited by the subsequent program.
+ *
+ * However the XENEVTCHN_NO_CLOEXEC flag may be used to avoid opening
+ * the device node with O_CLOEXEC. This is intended for use by
+ * daemons which support a self-reexec method of updating themselves.
+ *
+ * In this case, the updated daemon should pass the underlying file
+ * descriptor it inherited to xenevtchn_fdopen() to reconstruct the
+ * library handle.
*/
-/* Currently no flags are defined */
+
+/* Don't set O_CLOEXEC when opening event channel driver node. */
+#define XENEVTCHN_NO_CLOEXEC (1U <<0)
+
xenevtchn_handle *xenevtchn_open(struct xentoollog_logger *logger,
unsigned int flags);
+/* Flag XENEVTCHN_NO_CLOEXEC is rejected by xenevtchn_fdopen(). */
+xenevtchn_handle *xenevtchn_fdopen(struct xentoollog_logger *logger,
+ int fd, unsigned open_flags);
+
/*
- * Close a handle previously allocated with xenevtchn_open().
+ * Close a handle previously allocated with xenevtchn_{,fd}open().
*/
int xenevtchn_close(xenevtchn_handle *xce);
diff --git a/tools/libs/evtchn/Makefile b/tools/libs/evtchn/Makefile
index ad01a17b3d..b8c37b5b97 100644
--- a/tools/libs/evtchn/Makefile
+++ b/tools/libs/evtchn/Makefile
@@ -2,7 +2,7 @@ XEN_ROOT = $(CURDIR)/../../..
include $(XEN_ROOT)/tools/Rules.mk
MAJOR = 1
-MINOR = 1
+MINOR = 2
SRCS-y += core.c
SRCS-$(CONFIG_Linux) += linux.c
diff --git a/tools/libs/evtchn/core.c b/tools/libs/evtchn/core.c
index d3cc93e98f..abebf72559 100644
--- a/tools/libs/evtchn/core.c
+++ b/tools/libs/evtchn/core.c
@@ -30,18 +30,10 @@ static int all_restrict_cb(Xentoolcore__Active_Handle *ah,
domid_t domid)
return xenevtchn_restrict(xce, domid);
}
-xenevtchn_handle *xenevtchn_open(xentoollog_logger *logger, unsigned int flags)
+static xenevtchn_handle *xenevtchn_alloc_handle(xentoollog_logger *logger)
{
- xenevtchn_handle *xce;
- int rc;
-
- if ( flags )
- {
- errno = EINVAL;
- return NULL;
- }
+ xenevtchn_handle *xce = malloc(sizeof(*xce));
- xce = malloc(sizeof(*xce));
if ( !xce )
return NULL;
@@ -60,21 +52,59 @@ xenevtchn_handle *xenevtchn_open(xentoollog_logger *logger,
unsigned int flags)
goto err;
}
+ return xce;
+
+err:
+ xenevtchn_close(xce);
+ return NULL;
+}
+
+xenevtchn_handle *xenevtchn_open(xentoollog_logger *logger, unsigned int flags)
+{
+ xenevtchn_handle *xce;
+ int rc;
+
+ if ( flags & ~XENEVTCHN_NO_CLOEXEC )
+ {
+ errno = EINVAL;
+ return NULL;
+ }
+
+ xce = xenevtchn_alloc_handle(logger);
+ if ( !xce )
+ return NULL;
+
rc = osdep_evtchn_open(xce, flags);
if ( rc < 0 )
goto err;
return xce;
- err:
- xentoolcore__deregister_active_handle(&xce->tc_ah);
- osdep_evtchn_close(xce);
- xtl_logger_destroy(xce->logger_tofree);
- free(xce);
-
+err:
+ xenevtchn_close(xce);
return NULL;
}
+xenevtchn_handle *xenevtchn_fdopen(struct xentoollog_logger *logger,
+ int fd, unsigned int flags)
+{
+ xenevtchn_handle *xce;
+
+ if ( flags )
+ {
+ errno = EINVAL;
+ return NULL;
+ }
+
+ xce = xenevtchn_alloc_handle(logger);
+ if ( !xce )
+ return NULL;
+
+ xce->fd = fd;
+
+ return xce;
+}
+
int xenevtchn_close(xenevtchn_handle *xce)
{
int rc;
diff --git a/tools/libs/evtchn/freebsd.c b/tools/libs/evtchn/freebsd.c
index bb601f350f..7427ab2408 100644
--- a/tools/libs/evtchn/freebsd.c
+++ b/tools/libs/evtchn/freebsd.c
@@ -33,8 +33,13 @@
int osdep_evtchn_open(xenevtchn_handle *xce, unsigned int flags)
{
- int fd = open(EVTCHN_DEV, O_RDWR|O_CLOEXEC);
+ int open_flags = O_RDWR;
+ int fd;
+ if ( !(flags & XENEVTCHN_NO_CLOEXEC) )
+ open_flags |= O_CLOEXEC;
+
+ fd = open(EVTCHN_DEV, open_flags);
if ( fd == -1 )
return -1;
diff --git a/tools/libs/evtchn/libxenevtchn.map
b/tools/libs/evtchn/libxenevtchn.map
index 33a38f953a..4c180ea65d 100644
--- a/tools/libs/evtchn/libxenevtchn.map
+++ b/tools/libs/evtchn/libxenevtchn.map
@@ -21,3 +21,7 @@ VERS_1.1 {
global:
xenevtchn_restrict;
} VERS_1.0;
+VERS_1.2 {
+ global:
+ xenevtchn_fdopen;
+} VERS_1.1;
diff --git a/tools/libs/evtchn/linux.c b/tools/libs/evtchn/linux.c
index 62adc0e574..60bb75a791 100644
--- a/tools/libs/evtchn/linux.c
+++ b/tools/libs/evtchn/linux.c
@@ -36,8 +36,12 @@
int osdep_evtchn_open(xenevtchn_handle *xce, unsigned int flags)
{
- int fd = open("/dev/xen/evtchn", O_RDWR|O_CLOEXEC);
+ int open_flags = O_RDWR;
+ int fd;
+ if ( !(flags & XENEVTCHN_NO_CLOEXEC) )
+ open_flags |= O_CLOEXEC;
+ fd = open("/dev/xen/evtchn", open_flags);
if ( fd == -1 )
return -1;
diff --git a/tools/libs/evtchn/minios.c b/tools/libs/evtchn/minios.c
index 3afc8e2517..57f712ade3 100644
--- a/tools/libs/evtchn/minios.c
+++ b/tools/libs/evtchn/minios.c
@@ -69,6 +69,10 @@ static void port_dealloc(struct evtchn_port_info *port_info)
free(port_info);
}
+/*
+ * XENEVTCHN_NO_CLOEXEC is being ignored, as there is no exec() call supported
+ * in Mini-OS.
+ */
int osdep_evtchn_open(xenevtchn_handle *xce, unsigned int flags)
{
int fd = alloc_fd(FTYPE_EVTCHN);
--
2.26.2
