[Qemu-devel] [PATCH 0/5] pr-manager/qemu-pr-helper patches for QEMU 3.0

[Qemu-devel] [PATCH 0/5] pr-manager/qemu-pr-helper patches for QEMU 3.0

[Paolo Bonzini]

The first three patches are more or less trivial bugfixes.  The
last two allow libvirt to know the status of the qemu-pr-helper
process that is attached to a running QEMU instance.

Michal, can you check that the interface in the last two patches
is good for you?

Thanks,

Paolo

Paolo Bonzini (5):
  pr-helper: fix --socket-path default in help
  pr-helper: fix assertion failure on failed multipath PERSISTENT
    RESERVE IN
  pr-manager-helper: avoid SIGSEGV when writing to the socket fail
  pr-manager: add query-pr-managers QMP command
  pr-manager-helper: report event on connection/disconnection

 include/scsi/pr-manager.h |  2 ++
 qapi/block.json           | 51 +++++++++++++++++++++++++++++++++++++++
 scsi/pr-manager-helper.c  | 39 +++++++++++++++++++++++++-----
 scsi/pr-manager.c         | 45 ++++++++++++++++++++++++++++++++++
 scsi/qemu-pr-helper.c     | 21 ++++++++++------
 5 files changed, 144 insertions(+), 14 deletions(-)

-- 
2.17.1

[Qemu-devel] [PATCH 1/5] pr-helper: fix --socket-path default in help

[Paolo Bonzini]

Currently --help shows "(default '(null)')" for the -k/--socket-path
option.  Fix it by getting the default path in /var/run.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 scsi/qemu-pr-helper.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c
index d0f83176e1..4057cf355c 100644
--- a/scsi/qemu-pr-helper.c
+++ b/scsi/qemu-pr-helper.c
@@ -74,8 +74,16 @@ static int uid = -1;
 static int gid = -1;
 #endif
 
+static void compute_default_paths(void)
+{
+    if (!socket_path) {
+        socket_path = qemu_get_local_state_pathname("run/qemu-pr-helper.sock");
+    }
+}
+
 static void usage(const char *name)
 {
+    compute_default_paths();
     (printf) (
 "Usage: %s [OPTIONS] FILE\n"
 "Persistent Reservation helper program for QEMU\n"
@@ -845,13 +853,6 @@ static const char *socket_activation_validate_opts(void)
     return NULL;
 }
 
-static void compute_default_paths(void)
-{
-    if (!socket_path) {
-        socket_path = qemu_get_local_state_pathname("run/qemu-pr-helper.sock");
-    }
-}
-
 static void termsig_handler(int signum)
 {
     atomic_cmpxchg(&state, RUNNING, TERMINATE);
-- 
2.17.1

[Qemu-devel] [PATCH 2/5] pr-helper: fix assertion failure on failed multipath PERSISTENT RESERVE IN

[Paolo Bonzini]

The response size is expected to be zero if the SCSI status is not
"GOOD", but nothing was resetting it.

This can be reproduced simply by "sg_persist -s /dev/sdb" where /dev/sdb
in the guest is a scsi-block device corresponding to a multipath device
on the host.

Before:

  PR in (Read full status): Aborted command

and on the host:

  prh_write_response: Assertion `resp->sz == 0' failed.

After:

  PR in (Read full status): bad field in cdb or parameter list
  (perhaps unsupported service action)

Reported-by: Jiri Belka <jbelka@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 scsi/qemu-pr-helper.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c
index 4057cf355c..0218d65bbf 100644
--- a/scsi/qemu-pr-helper.c
+++ b/scsi/qemu-pr-helper.c
@@ -558,7 +558,11 @@ static int do_pr_in(int fd, const uint8_t *cdb, uint8_t *sense,
 #ifdef CONFIG_MPATH
     if (is_mpath(fd)) {
         /* multipath_pr_in fills the whole input buffer.  */
-        return multipath_pr_in(fd, cdb, sense, data, *resp_sz);
+        int r = multipath_pr_in(fd, cdb, sense, data, *resp_sz);
+        if (r != GOOD) {
+            *resp_sz = 0;
+        }
+        return r;
     }
 #endif
 
-- 
2.17.1

[Qemu-devel] [PATCH 3/5] pr-manager-helper: avoid SIGSEGV when writing to the socket fail

[Paolo Bonzini]

When writing to the qemu-pr-helper socket failed, the persistent
reservation manager was correctly disconnecting the socket, but it
did not clear pr_mgr->ioc.  So the rest of the code did not know
that the socket had been disconnected, accessed pr_mgr->ioc and
happily caused a crash.

To reproduce, it is enough to stop qemu-pr-helper between QEMU
startup and executing e.g. sg_persist -k /dev/sdb.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 scsi/pr-manager-helper.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scsi/pr-manager-helper.c b/scsi/pr-manager-helper.c
index 82ff6b6123..0c0fe389b7 100644
--- a/scsi/pr-manager-helper.c
+++ b/scsi/pr-manager-helper.c
@@ -71,6 +71,7 @@ static int pr_manager_helper_write(PRManagerHelper *pr_mgr,
         if (n_written <= 0) {
             assert(n_written != QIO_CHANNEL_ERR_BLOCK);
             object_unref(OBJECT(pr_mgr->ioc));
+            pr_mgr->ioc = NULL;
             return n_written < 0 ? -EINVAL : 0;
         }
 
-- 
2.17.1

[Qemu-devel] [PATCH 4/5] pr-manager: add query-pr-managers QMP command

[Paolo Bonzini]

This command lets you query the connection status of each pr-manager-helper
object.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 include/scsi/pr-manager.h |  2 ++
 qapi/block.json           | 27 +++++++++++++++++++++++
 scsi/pr-manager-helper.c  | 13 +++++++++++
 scsi/pr-manager.c         | 45 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 87 insertions(+)

diff --git a/include/scsi/pr-manager.h b/include/scsi/pr-manager.h
index 5d2f13a5e4..adadca7954 100644
--- a/include/scsi/pr-manager.h
+++ b/include/scsi/pr-manager.h
@@ -33,8 +33,10 @@ typedef struct PRManagerClass {
 
     /* <public> */
     int (*run)(PRManager *pr_mgr, int fd, struct sg_io_hdr *hdr);
+    bool (*is_connected)(PRManager *pr_mgr);
 } PRManagerClass;
 
+bool pr_manager_is_connected(PRManager *pr_mgr);
 BlockAIOCB *pr_manager_execute(PRManager *pr_mgr,
                                AioContext *ctx, int fd,
                                struct sg_io_hdr *hdr,
diff --git a/qapi/block.json b/qapi/block.json
index c694524002..dc3323c954 100644
--- a/qapi/block.json
+++ b/qapi/block.json
@@ -77,6 +77,33 @@
 { 'struct': 'BlockdevSnapshotInternal',
   'data': { 'device': 'str', 'name': 'str' } }
 
+##
+# @PRManagerInfo:
+#
+# Information about a persistent reservation manager
+#
+# @id: the identifier of the persistent reservation manager
+#
+# @is-connected: whether the persistent reservation manager is connected to
+#                the underlying storage or helper
+#
+# Since: 3.0
+##
+{ 'struct': 'PRManagerInfo',
+  'data': {'id': 'str', 'is-connected': 'bool'} }
+
+##
+# @query-pr-managers:
+#
+# Returns a list of information about each persistent reservation manager.
+#
+# Returns: a list of @PRManagerInfo for each persistent reservation manager
+#
+# Since: 3.0
+##
+{ 'command': 'query-pr-managers', 'returns': ['PRManagerInfo'] }
+
+
 ##
 # @blockdev-snapshot-internal-sync:
 #
diff --git a/scsi/pr-manager-helper.c b/scsi/pr-manager-helper.c
index 0c0fe389b7..b11481be9e 100644
--- a/scsi/pr-manager-helper.c
+++ b/scsi/pr-manager-helper.c
@@ -235,6 +235,18 @@ out:
     return ret;
 }
 
+static bool pr_manager_helper_is_connected(PRManager *p)
+{
+    PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(p);
+    bool result;
+
+    qemu_mutex_lock(&pr_mgr->lock);
+    result = (pr_mgr->ioc != NULL);
+    qemu_mutex_unlock(&pr_mgr->lock);
+
+    return result;
+}
+
 static void pr_manager_helper_complete(UserCreatable *uc, Error **errp)
 {
     PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(uc);
@@ -284,6 +296,7 @@ static void pr_manager_helper_class_init(ObjectClass *klass,
                                   &error_abort);
     uc_klass->complete = pr_manager_helper_complete;
     prmgr_klass->run = pr_manager_helper_run;
+    prmgr_klass->is_connected = pr_manager_helper_is_connected;
 }
 
 static const TypeInfo pr_manager_helper_info = {
diff --git a/scsi/pr-manager.c b/scsi/pr-manager.c
index 87c45db5d4..b6c3056cc3 100644
--- a/scsi/pr-manager.c
+++ b/scsi/pr-manager.c
@@ -17,6 +17,10 @@
 #include "block/thread-pool.h"
 #include "scsi/pr-manager.h"
 #include "trace.h"
+#include "qapi/qapi-types-block.h"
+#include "qapi/qapi-commands-block.h"
+
+#define PR_MANAGER_PATH     "/objects"
 
 typedef struct PRManagerData {
     PRManager *pr_mgr;
@@ -64,6 +68,14 @@ BlockAIOCB *pr_manager_execute(PRManager *pr_mgr,
                                   data, complete, opaque);
 }
 
+bool pr_manager_is_connected(PRManager *pr_mgr)
+{
+    PRManagerClass *pr_mgr_class =
+        PR_MANAGER_GET_CLASS(pr_mgr);
+
+    return !pr_mgr_class->is_connected || pr_mgr_class->is_connected(pr_mgr);
+}
+
 static const TypeInfo pr_manager_info = {
     .parent = TYPE_OBJECT,
     .name = TYPE_PR_MANAGER,
@@ -105,5 +117,38 @@ pr_manager_register_types(void)
     type_register_static(&pr_manager_info);
 }
 
+static int query_one_pr_manager(Object *object, void *opaque)
+{
+    PRManagerInfoList ***prev = opaque;
+    PRManagerInfoList *elem;
+    PRManagerInfo *info;
+    PRManager *pr_mgr;
+
+    pr_mgr = (PRManager *)object_dynamic_cast(object, TYPE_PR_MANAGER);
+    if (!pr_mgr) {
+        return 0;
+    }
+
+    elem = g_new0(PRManagerInfoList, 1);
+    info = g_new0(PRManagerInfo, 1);
+    info->id = object_get_canonical_path_component(object);
+    info->is_connected = pr_manager_is_connected(pr_mgr);
+    elem->value = info;
+    elem->next = NULL;
+
+    **prev = elem;
+    *prev = &elem->next;
+    return 0;
+}
+
+PRManagerInfoList *qmp_query_pr_managers(Error **errp)
+{
+    PRManagerInfoList *head = NULL;
+    PRManagerInfoList **prev = &head;
+    Object *container = container_get(object_get_root(), PR_MANAGER_PATH);
+
+    object_child_foreach(container, query_one_pr_manager, &prev);
+    return head;
+}
 
 type_init(pr_manager_register_types);
-- 
2.17.1

[Qemu-devel] [PATCH 5/5] pr-manager-helper: report event on connection/disconnection

[Paolo Bonzini]

Let management know if there were any problems communicating with
qemu-pr-helper.  The event is edge-triggered, and is sent every time
the connection status of the pr-manager-helper object changes.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 qapi/block.json          | 24 ++++++++++++++++++++++++
 scsi/pr-manager-helper.c | 25 +++++++++++++++++++------
 2 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/qapi/block.json b/qapi/block.json
index dc3323c954..1882a8d107 100644
--- a/qapi/block.json
+++ b/qapi/block.json
@@ -334,6 +334,30 @@
 { 'event': 'DEVICE_TRAY_MOVED',
   'data': { 'device': 'str', 'id': 'str', 'tray-open': 'bool' } }
 
+##
+# @PR_MANAGER_STATUS_CHANGED:
+#
+# Emitted whenever the connected status of a persistent reservation
+# manager changes.
+#
+# @id: The QOM path of the PR manager object
+#
+# @connected: true if the PR manager is connected to a backend
+#
+# Since: 2.12
+#
+# Example:
+#
+# <- { "event": "PR_MANAGER_STATUS_CHANGED",
+#      "data": { "id": "/object/pr-helper0",
+#                "connected": true
+#      },
+#      "timestamp": { "seconds": 1519840375, "microseconds": 450486 } }
+#
+##
+{ 'event': 'PR_MANAGER_STATUS_CHANGED',
+  'data': { 'id': 'str', 'connected': 'bool' } }
+
 ##
 # @QuorumOpType:
 #
diff --git a/scsi/pr-manager-helper.c b/scsi/pr-manager-helper.c
index b11481be9e..6643caf4cf 100644
--- a/scsi/pr-manager-helper.c
+++ b/scsi/pr-manager-helper.c
@@ -17,6 +17,7 @@
 #include "io/channel.h"
 #include "io/channel-socket.h"
 #include "pr-helper.h"
+#include "qapi/qapi-events-block.h"
 
 #include <scsi/sg.h>
 
@@ -33,6 +34,7 @@ typedef struct PRManagerHelper {
     PRManager parent;
 
     char *path;
+    char *qom_path;
 
     QemuMutex lock;
     QIOChannel *ioc;
@@ -127,6 +129,8 @@ static int pr_manager_helper_initialize(PRManagerHelper *pr_mgr,
         goto out_close;
     }
 
+    qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, true,
+                                              &error_abort);
     return 0;
 
 out_close:
@@ -142,9 +146,11 @@ static int pr_manager_helper_run(PRManager *p,
 
     uint32_t len;
     PRHelperResponse resp;
+    int sense_len;
     int ret;
     int expected_dir;
     int attempts;
+    bool was_connected = pr_mgr->ioc != NULL;
     uint8_t cdb[PR_HELPER_CDB_SIZE] = { 0 };
 
     if (!io_hdr->cmd_len || io_hdr->cmd_len > PR_HELPER_CDB_SIZE) {
@@ -222,15 +228,19 @@ static int pr_manager_helper_run(PRManager *p,
         io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, PR_HELPER_SENSE_SIZE);
         memcpy(io_hdr->sbp, resp.sense, io_hdr->sb_len_wr);
     }
+    qemu_mutex_unlock(&pr_mgr->lock);
+    return ret;
 
 out:
-    if (ret < 0) {
-        int sense_len = scsi_build_sense(io_hdr->sbp,
-                                         SENSE_CODE(LUN_COMM_FAILURE));
-        io_hdr->driver_status = SG_ERR_DRIVER_SENSE;
-        io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, sense_len);
-        io_hdr->status = CHECK_CONDITION;
+    if (was_connected) {
+        qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, false,
+                                                  &error_abort);
     }
+
+    sense_len = scsi_build_sense(io_hdr->sbp, SENSE_CODE(LUN_COMM_FAILURE));
+    io_hdr->driver_status = SG_ERR_DRIVER_SENSE;
+    io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, sense_len);
+    io_hdr->status = CHECK_CONDITION;
     qemu_mutex_unlock(&pr_mgr->lock);
     return ret;
 }
@@ -251,6 +261,8 @@ static void pr_manager_helper_complete(UserCreatable *uc, Error **errp)
 {
     PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(uc);
 
+    pr_mgr->qom_path = object_get_canonical_path(OBJECT(pr_mgr));
+
     qemu_mutex_lock(&pr_mgr->lock);
     pr_manager_helper_initialize(pr_mgr, errp);
     qemu_mutex_unlock(&pr_mgr->lock);
@@ -276,6 +288,7 @@ static void pr_manager_helper_instance_finalize(Object *obj)
     PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(obj);
 
     object_unref(OBJECT(pr_mgr->ioc));
+    g_free(pr_mgr->qom_path);
     qemu_mutex_destroy(&pr_mgr->lock);
 }
 
-- 
2.17.1

Re: [Qemu-devel] [PATCH 1/5] pr-helper: fix --socket-path default in help

[Philippe Mathieu-Daudé]

On 06/26/2018 12:40 PM, Paolo Bonzini wrote:
> Currently --help shows "(default '(null)')" for the -k/--socket-path
> option.  Fix it by getting the default path in /var/run.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

> ---
>  scsi/qemu-pr-helper.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c
> index d0f83176e1..4057cf355c 100644
> --- a/scsi/qemu-pr-helper.c
> +++ b/scsi/qemu-pr-helper.c
> @@ -74,8 +74,16 @@ static int uid = -1;
>  static int gid = -1;
>  #endif
>  
> +static void compute_default_paths(void)
> +{
> +    if (!socket_path) {
> +        socket_path = qemu_get_local_state_pathname("run/qemu-pr-helper.sock");
> +    }
> +}
> +
>  static void usage(const char *name)
>  {
> +    compute_default_paths();
>      (printf) (
>  "Usage: %s [OPTIONS] FILE\n"
>  "Persistent Reservation helper program for QEMU\n"
> @@ -845,13 +853,6 @@ static const char *socket_activation_validate_opts(void)
>      return NULL;
>  }
>  
> -static void compute_default_paths(void)
> -{
> -    if (!socket_path) {
> -        socket_path = qemu_get_local_state_pathname("run/qemu-pr-helper.sock");
> -    }
> -}
> -
>  static void termsig_handler(int signum)
>  {
>      atomic_cmpxchg(&state, RUNNING, TERMINATE);
> 

Re: [Qemu-devel] [PATCH 2/5] pr-helper: fix assertion failure on failed multipath PERSISTENT RESERVE IN

[Philippe Mathieu-Daudé]

On 06/26/2018 12:40 PM, Paolo Bonzini wrote:
> The response size is expected to be zero if the SCSI status is not
> "GOOD", but nothing was resetting it.
> 
> This can be reproduced simply by "sg_persist -s /dev/sdb" where /dev/sdb
> in the guest is a scsi-block device corresponding to a multipath device
> on the host.
> 
> Before:
> 
>   PR in (Read full status): Aborted command
> 
> and on the host:
> 
>   prh_write_response: Assertion `resp->sz == 0' failed.
> 
> After:
> 
>   PR in (Read full status): bad field in cdb or parameter list
>   (perhaps unsupported service action)
> 
> Reported-by: Jiri Belka <jbelka@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

> ---
>  scsi/qemu-pr-helper.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c
> index 4057cf355c..0218d65bbf 100644
> --- a/scsi/qemu-pr-helper.c
> +++ b/scsi/qemu-pr-helper.c
> @@ -558,7 +558,11 @@ static int do_pr_in(int fd, const uint8_t *cdb, uint8_t *sense,
>  #ifdef CONFIG_MPATH
>      if (is_mpath(fd)) {
>          /* multipath_pr_in fills the whole input buffer.  */
> -        return multipath_pr_in(fd, cdb, sense, data, *resp_sz);
> +        int r = multipath_pr_in(fd, cdb, sense, data, *resp_sz);
> +        if (r != GOOD) {
> +            *resp_sz = 0;
> +        }
> +        return r;
>      }
>  #endif
>  
> 

Re: [Qemu-devel] [PATCH 5/5] pr-manager-helper: report event on connection/disconnection

[Philippe Mathieu-Daudé]

Hi Paolo,

On 06/26/2018 12:40 PM, Paolo Bonzini wrote:
> Let management know if there were any problems communicating with
> qemu-pr-helper.  The event is edge-triggered, and is sent every time
> the connection status of the pr-manager-helper object changes.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  qapi/block.json          | 24 ++++++++++++++++++++++++
>  scsi/pr-manager-helper.c | 25 +++++++++++++++++++------
>  2 files changed, 43 insertions(+), 6 deletions(-)
> 
> diff --git a/qapi/block.json b/qapi/block.json
> index dc3323c954..1882a8d107 100644
> --- a/qapi/block.json
> +++ b/qapi/block.json
> @@ -334,6 +334,30 @@
>  { 'event': 'DEVICE_TRAY_MOVED',
>    'data': { 'device': 'str', 'id': 'str', 'tray-open': 'bool' } }
>  
> +##
> +# @PR_MANAGER_STATUS_CHANGED:
> +#
> +# Emitted whenever the connected status of a persistent reservation
> +# manager changes.
> +#
> +# @id: The QOM path of the PR manager object
> +#
> +# @connected: true if the PR manager is connected to a backend
> +#
> +# Since: 2.12

3.0?

> +#
> +# Example:
> +#
> +# <- { "event": "PR_MANAGER_STATUS_CHANGED",
> +#      "data": { "id": "/object/pr-helper0",
> +#                "connected": true
> +#      },
> +#      "timestamp": { "seconds": 1519840375, "microseconds": 450486 } }
> +#
> +##
> +{ 'event': 'PR_MANAGER_STATUS_CHANGED',
> +  'data': { 'id': 'str', 'connected': 'bool' } }
> +
>  ##
>  # @QuorumOpType:
>  #
> diff --git a/scsi/pr-manager-helper.c b/scsi/pr-manager-helper.c
> index b11481be9e..6643caf4cf 100644
> --- a/scsi/pr-manager-helper.c
> +++ b/scsi/pr-manager-helper.c
> @@ -17,6 +17,7 @@
>  #include "io/channel.h"
>  #include "io/channel-socket.h"
>  #include "pr-helper.h"
> +#include "qapi/qapi-events-block.h"
>  
>  #include <scsi/sg.h>
>  
> @@ -33,6 +34,7 @@ typedef struct PRManagerHelper {
>      PRManager parent;
>  
>      char *path;
> +    char *qom_path;
>  
>      QemuMutex lock;
>      QIOChannel *ioc;
> @@ -127,6 +129,8 @@ static int pr_manager_helper_initialize(PRManagerHelper *pr_mgr,
>          goto out_close;
>      }
>  
> +    qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, true,
> +                                              &error_abort);
>      return 0;
>  
>  out_close:
> @@ -142,9 +146,11 @@ static int pr_manager_helper_run(PRManager *p,
>  
>      uint32_t len;
>      PRHelperResponse resp;
> +    int sense_len;
>      int ret;
>      int expected_dir;
>      int attempts;
> +    bool was_connected = pr_mgr->ioc != NULL;
>      uint8_t cdb[PR_HELPER_CDB_SIZE] = { 0 };
>  
>      if (!io_hdr->cmd_len || io_hdr->cmd_len > PR_HELPER_CDB_SIZE) {
> @@ -222,15 +228,19 @@ static int pr_manager_helper_run(PRManager *p,
>          io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, PR_HELPER_SENSE_SIZE);
>          memcpy(io_hdr->sbp, resp.sense, io_hdr->sb_len_wr);
>      }
> +    qemu_mutex_unlock(&pr_mgr->lock);
> +    return ret;

Maybe this big function can be refactored in 2, the second being the
bottom code with the mutex locked.

>  
>  out:
> -    if (ret < 0) {
> -        int sense_len = scsi_build_sense(io_hdr->sbp,
> -                                         SENSE_CODE(LUN_COMM_FAILURE));
> -        io_hdr->driver_status = SG_ERR_DRIVER_SENSE;
> -        io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, sense_len);
> -        io_hdr->status = CHECK_CONDITION;
> +    if (was_connected) {
> +        qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, false,
> +                                                  &error_abort);
>      }
> +
> +    sense_len = scsi_build_sense(io_hdr->sbp, SENSE_CODE(LUN_COMM_FAILURE));
> +    io_hdr->driver_status = SG_ERR_DRIVER_SENSE;
> +    io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, sense_len);
> +    io_hdr->status = CHECK_CONDITION;
>      qemu_mutex_unlock(&pr_mgr->lock);
>      return ret;
>  }
> @@ -251,6 +261,8 @@ static void pr_manager_helper_complete(UserCreatable *uc, Error **errp)
>  {
>      PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(uc);
>  
> +    pr_mgr->qom_path = object_get_canonical_path(OBJECT(pr_mgr));
> +
>      qemu_mutex_lock(&pr_mgr->lock);
>      pr_manager_helper_initialize(pr_mgr, errp);
>      qemu_mutex_unlock(&pr_mgr->lock);
> @@ -276,6 +288,7 @@ static void pr_manager_helper_instance_finalize(Object *obj)
>      PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(obj);
>  
>      object_unref(OBJECT(pr_mgr->ioc));
> +    g_free(pr_mgr->qom_path);
>      qemu_mutex_destroy(&pr_mgr->lock);
>  }
>  
> 

Re: [Qemu-devel] [PATCH 1/5] pr-helper: fix --socket-path default in help

[Michal Privoznik]

On 06/26/2018 05:40 PM, Paolo Bonzini wrote:
> Currently --help shows "(default '(null)')" for the -k/--socket-path
> option.  Fix it by getting the default path in /var/run.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  scsi/qemu-pr-helper.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c
> index d0f83176e1..4057cf355c 100644
> --- a/scsi/qemu-pr-helper.c
> +++ b/scsi/qemu-pr-helper.c
> @@ -74,8 +74,16 @@ static int uid = -1;
>  static int gid = -1;
>  #endif
>  
> +static void compute_default_paths(void)
> +{
> +    if (!socket_path) {
> +        socket_path = qemu_get_local_state_pathname("run/qemu-pr-helper.sock");
> +    }
> +}
> +

Pre-existing, but pidfile path is computed elsewhere. I'll post a patch
that cleans things up. Not a show stopper for this one though.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

Michal

Re: [Qemu-devel] [PATCH 3/5] pr-manager-helper: avoid SIGSEGV when writing to the socket fail

[Michal Privoznik]

On 06/26/2018 05:40 PM, Paolo Bonzini wrote:
> When writing to the qemu-pr-helper socket failed, the persistent
> reservation manager was correctly disconnecting the socket, but it
> did not clear pr_mgr->ioc.  So the rest of the code did not know
> that the socket had been disconnected, accessed pr_mgr->ioc and
> happily caused a crash.
> 
> To reproduce, it is enough to stop qemu-pr-helper between QEMU
> startup and executing e.g. sg_persist -k /dev/sdb.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  scsi/pr-manager-helper.c | 1 +
>  1 file changed, 1 insertion(+)

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

Michal

Re: [Qemu-devel] [PATCH 2/5] pr-helper: fix assertion failure on failed multipath PERSISTENT RESERVE IN

[Michal Privoznik]

On 06/26/2018 05:40 PM, Paolo Bonzini wrote:
> The response size is expected to be zero if the SCSI status is not
> "GOOD", but nothing was resetting it.
> 
> This can be reproduced simply by "sg_persist -s /dev/sdb" where /dev/sdb
> in the guest is a scsi-block device corresponding to a multipath device
> on the host.
> 
> Before:
> 
>   PR in (Read full status): Aborted command
> 
> and on the host:
> 
>   prh_write_response: Assertion `resp->sz == 0' failed.
> 
> After:
> 
>   PR in (Read full status): bad field in cdb or parameter list
>   (perhaps unsupported service action)
> 
> Reported-by: Jiri Belka <jbelka@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  scsi/qemu-pr-helper.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

Michal

Re: [Qemu-devel] [PATCH 4/5] pr-manager: add query-pr-managers QMP command

[Michal Privoznik]

On 06/26/2018 05:40 PM, Paolo Bonzini wrote:
> This command lets you query the connection status of each pr-manager-helper
> object.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  include/scsi/pr-manager.h |  2 ++
>  qapi/block.json           | 27 +++++++++++++++++++++++
>  scsi/pr-manager-helper.c  | 13 +++++++++++
>  scsi/pr-manager.c         | 45 +++++++++++++++++++++++++++++++++++++++
>  4 files changed, 87 insertions(+)
> 
> diff --git a/include/scsi/pr-manager.h b/include/scsi/pr-manager.h
> index 5d2f13a5e4..adadca7954 100644
> --- a/include/scsi/pr-manager.h
> +++ b/include/scsi/pr-manager.h
> @@ -33,8 +33,10 @@ typedef struct PRManagerClass {
>  
>      /* <public> */
>      int (*run)(PRManager *pr_mgr, int fd, struct sg_io_hdr *hdr);
> +    bool (*is_connected)(PRManager *pr_mgr);
>  } PRManagerClass;
>  
> +bool pr_manager_is_connected(PRManager *pr_mgr);
>  BlockAIOCB *pr_manager_execute(PRManager *pr_mgr,
>                                 AioContext *ctx, int fd,
>                                 struct sg_io_hdr *hdr,
> diff --git a/qapi/block.json b/qapi/block.json
> index c694524002..dc3323c954 100644
> --- a/qapi/block.json
> +++ b/qapi/block.json
> @@ -77,6 +77,33 @@
>  { 'struct': 'BlockdevSnapshotInternal',
>    'data': { 'device': 'str', 'name': 'str' } }
>  
> +##
> +# @PRManagerInfo:
> +#
> +# Information about a persistent reservation manager
> +#
> +# @id: the identifier of the persistent reservation manager
> +#
> +# @is-connected: whether the persistent reservation manager is connected to
> +#                the underlying storage or helper
> +#
> +# Since: 3.0
> +##
> +{ 'struct': 'PRManagerInfo',
> +  'data': {'id': 'str', 'is-connected': 'bool'} }
> +
> +##
> +# @query-pr-managers:
> +#
> +# Returns a list of information about each persistent reservation manager.
> +#
> +# Returns: a list of @PRManagerInfo for each persistent reservation manager
> +#
> +# Since: 3.0
> +##
> +{ 'command': 'query-pr-managers', 'returns': ['PRManagerInfo'] }
> +
> +
>  ##
>  # @blockdev-snapshot-internal-sync:
>  #
> diff --git a/scsi/pr-manager-helper.c b/scsi/pr-manager-helper.c
> index 0c0fe389b7..b11481be9e 100644
> --- a/scsi/pr-manager-helper.c
> +++ b/scsi/pr-manager-helper.c
> @@ -235,6 +235,18 @@ out:
>      return ret;
>  }
>  
> +static bool pr_manager_helper_is_connected(PRManager *p)
> +{
> +    PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(p);
> +    bool result;
> +
> +    qemu_mutex_lock(&pr_mgr->lock);
> +    result = (pr_mgr->ioc != NULL);

I worry it is not that easy. pr_mgr->ioc is unset only when there's
PR_IN/PR_OUT command coming from the guest (in pr_manager_helper_run ->
pr_manager_helper_write). In fact, after 5/5 that is also the time when
the event is delivered. But that might be too late for mgmt app to
restart the helper process (although pr_manager_helper_run() tries to
reconnect for 5 seconds before giving up).

The patch is good code-wise though.

Michal

Re: [Qemu-devel] [PATCH 4/5] pr-manager: add query-pr-managers QMP command

[Eric Blake]

On 06/26/2018 10:40 AM, Paolo Bonzini wrote:
> This command lets you query the connection status of each pr-manager-helper
> object.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

> +++ b/qapi/block.json
> @@ -77,6 +77,33 @@
>   { 'struct': 'BlockdevSnapshotInternal',
>     'data': { 'device': 'str', 'name': 'str' } }
>   
> +##
> +# @PRManagerInfo:
> +#
> +# Information about a persistent reservation manager
> +#
> +# @id: the identifier of the persistent reservation manager
> +#
> +# @is-connected: whether the persistent reservation manager is connected to
> +#                the underlying storage or helper
> +#
> +# Since: 3.0
> +##
> +{ 'struct': 'PRManagerInfo',
> +  'data': {'id': 'str', 'is-connected': 'bool'} }

Bike-shedding: I think 'connected' is a reasonable (and shorter) name 
for this member

> +
> +##
> +# @query-pr-managers:
> +#
> +# Returns a list of information about each persistent reservation manager.
> +#
> +# Returns: a list of @PRManagerInfo for each persistent reservation manager
> +#
> +# Since: 3.0
> +##
> +{ 'command': 'query-pr-managers', 'returns': ['PRManagerInfo'] }
> +

As a query command, does it make sense to consider whether this command 
could be provided during preconfig?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCH 5/5] pr-manager-helper: report event on connection/disconnection

[Michal Privoznik]

On 06/26/2018 05:40 PM, Paolo Bonzini wrote:
> Let management know if there were any problems communicating with
> qemu-pr-helper.  The event is edge-triggered, and is sent every time
> the connection status of the pr-manager-helper object changes.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  qapi/block.json          | 24 ++++++++++++++++++++++++
>  scsi/pr-manager-helper.c | 25 +++++++++++++++++++------
>  2 files changed, 43 insertions(+), 6 deletions(-)
> 
> diff --git a/qapi/block.json b/qapi/block.json
> index dc3323c954..1882a8d107 100644
> --- a/qapi/block.json
> +++ b/qapi/block.json
> @@ -334,6 +334,30 @@
>  { 'event': 'DEVICE_TRAY_MOVED',
>    'data': { 'device': 'str', 'id': 'str', 'tray-open': 'bool' } }
>  
> +##
> +# @PR_MANAGER_STATUS_CHANGED:
> +#
> +# Emitted whenever the connected status of a persistent reservation
> +# manager changes.
> +#
> +# @id: The QOM path of the PR manager object
> +#
> +# @connected: true if the PR manager is connected to a backend
> +#
> +# Since: 2.12
> +#
> +# Example:
> +#
> +# <- { "event": "PR_MANAGER_STATUS_CHANGED",
> +#      "data": { "id": "/object/pr-helper0",
> +#                "connected": true
> +#      },
> +#      "timestamp": { "seconds": 1519840375, "microseconds": 450486 } }
> +#
> +##
> +{ 'event': 'PR_MANAGER_STATUS_CHANGED',
> +  'data': { 'id': 'str', 'connected': 'bool' } }
> +
>  ##
>  # @QuorumOpType:
>  #
> diff --git a/scsi/pr-manager-helper.c b/scsi/pr-manager-helper.c
> index b11481be9e..6643caf4cf 100644
> --- a/scsi/pr-manager-helper.c
> +++ b/scsi/pr-manager-helper.c
> @@ -17,6 +17,7 @@
>  #include "io/channel.h"
>  #include "io/channel-socket.h"
>  #include "pr-helper.h"
> +#include "qapi/qapi-events-block.h"
>  
>  #include <scsi/sg.h>
>  
> @@ -33,6 +34,7 @@ typedef struct PRManagerHelper {
>      PRManager parent;
>  
>      char *path;
> +    char *qom_path;
>  
>      QemuMutex lock;
>      QIOChannel *ioc;
> @@ -127,6 +129,8 @@ static int pr_manager_helper_initialize(PRManagerHelper *pr_mgr,
>          goto out_close;
>      }
>  
> +    qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, true,
> +                                              &error_abort);
>      return 0;
>  
>  out_close:
> @@ -142,9 +146,11 @@ static int pr_manager_helper_run(PRManager *p,
>  
>      uint32_t len;
>      PRHelperResponse resp;
> +    int sense_len;
>      int ret;
>      int expected_dir;
>      int attempts;
> +    bool was_connected = pr_mgr->ioc != NULL;
>      uint8_t cdb[PR_HELPER_CDB_SIZE] = { 0 };
>  
>      if (!io_hdr->cmd_len || io_hdr->cmd_len > PR_HELPER_CDB_SIZE) {
> @@ -222,15 +228,19 @@ static int pr_manager_helper_run(PRManager *p,
>          io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, PR_HELPER_SENSE_SIZE);
>          memcpy(io_hdr->sbp, resp.sense, io_hdr->sb_len_wr);
>      }
> +    qemu_mutex_unlock(&pr_mgr->lock);
> +    return ret;
>  
>  out:
> -    if (ret < 0) {
> -        int sense_len = scsi_build_sense(io_hdr->sbp,
> -                                         SENSE_CODE(LUN_COMM_FAILURE));
> -        io_hdr->driver_status = SG_ERR_DRIVER_SENSE;
> -        io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, sense_len);
> -        io_hdr->status = CHECK_CONDITION;
> +    if (was_connected) {
> +        qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, false,
> +                                                  &error_abort);
>      }
> +
> +    sense_len = scsi_build_sense(io_hdr->sbp, SENSE_CODE(LUN_COMM_FAILURE));
> +    io_hdr->driver_status = SG_ERR_DRIVER_SENSE;
> +    io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, sense_len);
> +    io_hdr->status = CHECK_CONDITION;
>      qemu_mutex_unlock(&pr_mgr->lock);
>      return ret;
>  }
> @@ -251,6 +261,8 @@ static void pr_manager_helper_complete(UserCreatable *uc, Error **errp)
>  {
>      PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(uc);
>  
> +    pr_mgr->qom_path = object_get_canonical_path(OBJECT(pr_mgr));

Might be worth returning just object_get_canonical_path_component() so
that the event looks like this:

{"event": "PR_MANAGER_STATUS_CHANGED", "data": {"connected": false,
"id": "pr-helper0"}}

(instead of full /object/pr-helper0 path). This corresponds to what
'query-pr-managers' returns too.

Michal

Re: [Qemu-devel] [PATCH 5/5] pr-manager-helper: report event on connection/disconnection

[Michal Privoznik]

On 06/26/2018 05:40 PM, Paolo Bonzini wrote:
> Let management know if there were any problems communicating with
> qemu-pr-helper.  The event is edge-triggered, and is sent every time
> the connection status of the pr-manager-helper object changes.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  qapi/block.json          | 24 ++++++++++++++++++++++++
>  scsi/pr-manager-helper.c | 25 +++++++++++++++++++------
>  2 files changed, 43 insertions(+), 6 deletions(-)
> 
> diff --git a/qapi/block.json b/qapi/block.json
> index dc3323c954..1882a8d107 100644
> --- a/qapi/block.json
> +++ b/qapi/block.json
> @@ -334,6 +334,30 @@
>  { 'event': 'DEVICE_TRAY_MOVED',
>    'data': { 'device': 'str', 'id': 'str', 'tray-open': 'bool' } }
>  
> +##
> +# @PR_MANAGER_STATUS_CHANGED:
> +#
> +# Emitted whenever the connected status of a persistent reservation
> +# manager changes.
> +#
> +# @id: The QOM path of the PR manager object
> +#
> +# @connected: true if the PR manager is connected to a backend
> +#
> +# Since: 2.12
> +#
> +# Example:
> +#
> +# <- { "event": "PR_MANAGER_STATUS_CHANGED",
> +#      "data": { "id": "/object/pr-helper0",
> +#                "connected": true
> +#      },
> +#      "timestamp": { "seconds": 1519840375, "microseconds": 450486 } }
> +#
> +##
> +{ 'event': 'PR_MANAGER_STATUS_CHANGED',
> +  'data': { 'id': 'str', 'connected': 'bool' } }
> +
>  ##
>  # @QuorumOpType:
>  #
> diff --git a/scsi/pr-manager-helper.c b/scsi/pr-manager-helper.c
> index b11481be9e..6643caf4cf 100644
> --- a/scsi/pr-manager-helper.c
> +++ b/scsi/pr-manager-helper.c
> @@ -17,6 +17,7 @@
>  #include "io/channel.h"
>  #include "io/channel-socket.h"
>  #include "pr-helper.h"
> +#include "qapi/qapi-events-block.h"
>  
>  #include <scsi/sg.h>
>  
> @@ -33,6 +34,7 @@ typedef struct PRManagerHelper {
>      PRManager parent;
>  
>      char *path;
> +    char *qom_path;
>  
>      QemuMutex lock;
>      QIOChannel *ioc;
> @@ -127,6 +129,8 @@ static int pr_manager_helper_initialize(PRManagerHelper *pr_mgr,
>          goto out_close;
>      }
>  
> +    qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, true,
> +                                              &error_abort);
>      return 0;

Also, can we emit this earlier? For instance at the two places where we
unset pr_mgr->ioc:

diff --git i/scsi/pr-manager-helper.c w/scsi/pr-manager-helper.c
index 6643caf4cf..4ca15dff3f 100644
--- i/scsi/pr-manager-helper.c
+++ w/scsi/pr-manager-helper.c
@@ -48,6 +48,8 @@ static int pr_manager_helper_read(PRManagerHelper *pr_mgr,
 
     if (r < 0) {
         object_unref(OBJECT(pr_mgr->ioc));
+        qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, false,
+                                                  &error_abort);
         pr_mgr->ioc = NULL;
         return -EINVAL;
     }
@@ -74,6 +76,8 @@ static int pr_manager_helper_write(PRManagerHelper *pr_mgr,
             assert(n_written != QIO_CHANNEL_ERR_BLOCK);
             object_unref(OBJECT(pr_mgr->ioc));
             pr_mgr->ioc = NULL;
+            qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, false,
+                                                      &error_abort);
             return n_written < 0 ? -EINVAL : 0;
         }
 
@@ -150,7 +154,6 @@ static int pr_manager_helper_run(PRManager *p,
     int ret;
     int expected_dir;
     int attempts;
-    bool was_connected = pr_mgr->ioc != NULL;
     uint8_t cdb[PR_HELPER_CDB_SIZE] = { 0 };
 
     if (!io_hdr->cmd_len || io_hdr->cmd_len > PR_HELPER_CDB_SIZE) {
@@ -232,11 +235,6 @@ static int pr_manager_helper_run(PRManager *p,
     return ret;
 
 out:
-    if (was_connected) {
-        qapi_event_send_pr_manager_status_changed(pr_mgr->qom_path, false,
-                                                  &error_abort);
-    }
-
     sense_len = scsi_build_sense(io_hdr->sbp, SENSE_CODE(LUN_COMM_FAILURE));
     io_hdr->driver_status = SG_ERR_DRIVER_SENSE;
     io_hdr->sb_len_wr = MIN(io_hdr->mx_sb_len, sense_len);
@@ -261,7 +259,7 @@ static void pr_manager_helper_complete(UserCreatable *uc, Error **errp)
 {
     PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(uc);
 
-    pr_mgr->qom_path = object_get_canonical_path(OBJECT(pr_mgr));
+    pr_mgr->qom_path = object_get_canonical_path_component(OBJECT(pr_mgr));
 
     qemu_mutex_lock(&pr_mgr->lock);
     pr_manager_helper_initialize(pr_mgr, errp);


With your approach the event is emitted only after the 5 reconnect 
attempts (which makes little sense IMO). With my approach the event is 
emitted a bit sooner so that reconnect has at least chance of 
succeeding.

I've written some patches for libvirt and with these changes it works 
well.

Michal

Re: [Qemu-devel] [PATCH 4/5] pr-manager: add query-pr-managers QMP command

[Paolo Bonzini]

On 26/06/2018 22:51, Eric Blake wrote:
> On 06/26/2018 10:40 AM, Paolo Bonzini wrote:
>> This command lets you query the connection status of each
>> pr-manager-helper
>> object.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
> 
>> +++ b/qapi/block.json
>> @@ -77,6 +77,33 @@
>>   { 'struct': 'BlockdevSnapshotInternal',
>>     'data': { 'device': 'str', 'name': 'str' } }
>>   +##
>> +# @PRManagerInfo:
>> +#
>> +# Information about a persistent reservation manager
>> +#
>> +# @id: the identifier of the persistent reservation manager
>> +#
>> +# @is-connected: whether the persistent reservation manager is
>> connected to
>> +#                the underlying storage or helper
>> +#
>> +# Since: 3.0
>> +##
>> +{ 'struct': 'PRManagerInfo',
>> +  'data': {'id': 'str', 'is-connected': 'bool'} }
> 
> Bike-shedding: I think 'connected' is a reasonable (and shorter) name
> for this member

Sounds good.

>> +
>> +##
>> +# @query-pr-managers:
>> +#
>> +# Returns a list of information about each persistent reservation
>> manager.
>> +#
>> +# Returns: a list of @PRManagerInfo for each persistent reservation
>> manager
>> +#
>> +# Since: 3.0
>> +##
>> +{ 'command': 'query-pr-managers', 'returns': ['PRManagerInfo'] }
>> +
> 
> As a query command, does it make sense to consider whether this command
> could be provided during preconfig?

Yes, definitely.

Paolo

Re: [Qemu-devel] [PATCH 5/5] pr-manager-helper: report event on connection/disconnection

[Paolo Bonzini]

On 27/06/2018 12:16, Michal Privoznik wrote:
> Also, can we emit this earlier? For instance at the two places where we
> unset pr_mgr->ioc:
> 
> With your approach the event is emitted only after the 5 reconnect 
> attempts (which makes little sense IMO). With my approach the event is 
> emitted a bit sooner so that reconnect has at least chance of 
> succeeding.

Much better, yes.  I included your change.

Paolo

Re: [Qemu-devel] [PATCH 4/5] pr-manager: add query-pr-managers QMP command

[Paolo Bonzini]

On 26/06/2018 18:31, Michal Privoznik wrote:
>>  
>> +static bool pr_manager_helper_is_connected(PRManager *p)
>> +{
>> +    PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(p);
>> +    bool result;
>> +
>> +    qemu_mutex_lock(&pr_mgr->lock);
>> +    result = (pr_mgr->ioc != NULL);
> I worry it is not that easy. pr_mgr->ioc is unset only when there's
> PR_IN/PR_OUT command coming from the guest (in pr_manager_helper_run ->
> pr_manager_helper_write). In fact, after 5/5 that is also the time when
> the event is delivered. But that might be too late for mgmt app to
> restart the helper process (although pr_manager_helper_run() tries to
> reconnect for 5 seconds before giving up).

That's true, however the important thing IMO is to have a QMP interface
that libvirt can use; everything else is just quality of implementation.

qemu-pr-helper anyway does something only when a guests sends it a PR
command - and with libvirt's per-guest model, that would (hopefully)
mean that the only case that remains is when someone manually kills the
qemu-pr-helper process.  In that case there's a certain amount of PEBKAC
involved... :)

Paolo

> The patch is good code-wise though.

Re: [Qemu-devel] [PATCH 4/5] pr-manager: add query-pr-managers QMP command

[Michal Prívozník]

On 06/27/2018 05:44 PM, Paolo Bonzini wrote:
> On 26/06/2018 18:31, Michal Privoznik wrote:
>>>  
>>> +static bool pr_manager_helper_is_connected(PRManager *p)
>>> +{
>>> +    PRManagerHelper *pr_mgr = PR_MANAGER_HELPER(p);
>>> +    bool result;
>>> +
>>> +    qemu_mutex_lock(&pr_mgr->lock);
>>> +    result = (pr_mgr->ioc != NULL);
>> I worry it is not that easy. pr_mgr->ioc is unset only when there's
>> PR_IN/PR_OUT command coming from the guest (in pr_manager_helper_run ->
>> pr_manager_helper_write). In fact, after 5/5 that is also the time when
>> the event is delivered. But that might be too late for mgmt app to
>> restart the helper process (although pr_manager_helper_run() tries to
>> reconnect for 5 seconds before giving up).
> 
> That's true, however the important thing IMO is to have a QMP interface
> that libvirt can use; everything else is just quality of implementation.
> 
> qemu-pr-helper anyway does something only when a guests sends it a PR
> command - and with libvirt's per-guest model, that would (hopefully)
> mean that the only case that remains is when someone manually kills the
> qemu-pr-helper process.  In that case there's a certain amount of PEBKAC
> involved... :)

Unless an assert() is triggered ;-)

But since you merged my suggested changes in 5/5 libvirt can catch the
event pretty soon, so in my testing qemu was still left with 3-4
connection retries which is plenty.

Michal

Re: [Qemu-devel] [PATCH 4/5] pr-manager: add query-pr-managers QMP command

[Paolo Bonzini]

On 28/06/2018 09:05, Michal Prívozník wrote:
>> qemu-pr-helper anyway does something only when a guests sends it a PR
>> command - and with libvirt's per-guest model, that would (hopefully)
>> mean that the only case that remains is when someone manually kills the
>> qemu-pr-helper process.  In that case there's a certain amount of PEBKAC
>> involved... :)
>
> Unless an assert() is triggered ;-)

Indeed, but that should still happen "when a guest sends it a PR
command".  The problematic case would only arise if qemu-pr-helper
crashes between the last time QEMU sent a command, and the time libvirt
sends query-pr-managers.

> But since you merged my suggested changes in 5/5 libvirt can catch the
> event pretty soon, so in my testing qemu was still left with 3-4
> connection retries which is plenty.

Good, thanks.

Paolo