[v5,02/10] kvm: Support for querying fd-based stats

From: Mark Kanda <mark.kanda@oracle.com>

Add support for querying fd-based KVM stats - as introduced by Linux kernel
commit:

cb082bfab59a ("KVM: stats: Add fd-based API to read binary stats data")

This allows the user to analyze the behavior of the VM without access
to debugfs.

Signed-off-by: Mark Kanda <mark.kanda@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 accel/kvm/kvm-all.c | 397 ++++++++++++++++++++++++++++++++++++++++++++
 qapi/stats.json     |   2 +-
 2 files changed, 398 insertions(+), 1 deletion(-)

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> From: Mark Kanda <mark.kanda@oracle.com>
> 
> Add support for querying fd-based KVM stats - as introduced by Linux kernel
> commit:
> 
> cb082bfab59a ("KVM: stats: Add fd-based API to read binary stats data")
> 
> This allows the user to analyze the behavior of the VM without access
> to debugfs.
> 
> Signed-off-by: Mark Kanda <mark.kanda@oracle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  accel/kvm/kvm-all.c | 397 ++++++++++++++++++++++++++++++++++++++++++++
>  qapi/stats.json     |   2 +-
>  2 files changed, 398 insertions(+), 1 deletion(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 32e177bd26..c027536419 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -47,6 +47,7 @@
>  #include "kvm-cpus.h"
>  
>  #include "hw/boards.h"
> +#include "monitor/stats.h"
>  
>  /* This check must be after config-host.h is included */
>  #ifdef CONFIG_EVENTFD
> @@ -2310,6 +2311,9 @@ bool kvm_dirty_ring_enabled(void)
>      return kvm_state->kvm_dirty_ring_size ? true : false;
>  }
>  
> +static void query_stats_cb(StatsResultList **result, StatsTarget target, Error **errp);
> +static void query_stats_schemas_cb(StatsSchemaList **result, Error **errp);
> +
>  static int kvm_init(MachineState *ms)
>  {
>      MachineClass *mc = MACHINE_GET_CLASS(ms);
> @@ -2638,6 +2642,10 @@ static int kvm_init(MachineState *ms)
>          }
>      }
>  
> +    if (kvm_check_extension(kvm_state, KVM_CAP_BINARY_STATS_FD)) {
> +        add_stats_callbacks(query_stats_cb, query_stats_schemas_cb);
> +    }
> +
>      return 0;
>  
>  err:
> @@ -3697,3 +3705,392 @@ static void kvm_type_init(void)
>  }
>  
>  type_init(kvm_type_init);
> +
> +typedef struct StatsArgs {
> +    union StatsResultsType {
> +        StatsResultList **stats;
> +        StatsSchemaList **schema;
> +    } result;
> +    Error **errp;
> +} StatsArgs;
> +
> +static StatsList *add_kvmstat_entry(struct kvm_stats_desc *pdesc,
> +                                    uint64_t *stats_data,
> +                                    StatsList *stats_list,
> +                                    Error **errp)
> +{
> +
> +    Stats *stats;
> +    uint64List *val_list = NULL;
> +
> +    /* Only add stats that we understand.  */
> +    switch (pdesc->flags & KVM_STATS_TYPE_MASK) {
> +    case KVM_STATS_TYPE_CUMULATIVE:
> +    case KVM_STATS_TYPE_INSTANT:
> +    case KVM_STATS_TYPE_PEAK:
> +    case KVM_STATS_TYPE_LINEAR_HIST:
> +    case KVM_STATS_TYPE_LOG_HIST:
> +        break;
> +    default:
> +        return stats_list;
> +    }
> +
> +    switch (pdesc->flags & KVM_STATS_UNIT_MASK) {
> +    case KVM_STATS_UNIT_NONE:
> +    case KVM_STATS_UNIT_BYTES:
> +    case KVM_STATS_UNIT_CYCLES:
> +    case KVM_STATS_UNIT_SECONDS:
> +        break;
> +    default:
> +        return stats_list;
> +    }
> +
> +    switch (pdesc->flags & KVM_STATS_BASE_MASK) {
> +    case KVM_STATS_BASE_POW10:
> +    case KVM_STATS_BASE_POW2:
> +        break;
> +    default:
> +        return stats_list;
> +    }
> +
> +    /* Alloc and populate data list */
> +    stats = g_new0(Stats, 1);
> +    stats->name = g_strdup(pdesc->name);
> +    stats->value = g_new0(StatsValue, 1);;
> +
> +    if (pdesc->size == 1) {
> +        stats->value->u.scalar = *stats_data;
> +        stats->value->type = QTYPE_QNUM;
> +    } else {
> +        int i;
> +        for (i = 0; i < pdesc->size; i++) {
> +            QAPI_LIST_PREPEND(val_list, stats_data[i]);
> +        }
> +        stats->value->u.list = val_list;
> +        stats->value->type = QTYPE_QLIST;
> +    }
> +
> +    QAPI_LIST_PREPEND(stats_list, stats);
> +    return stats_list;
> +}
> +
> +static StatsSchemaValueList *add_kvmschema_entry(struct kvm_stats_desc *pdesc,
> +                                                 StatsSchemaValueList *list,
> +                                                 Error **errp)
> +{
> +    StatsSchemaValueList *schema_entry = g_new0(StatsSchemaValueList, 1);
> +    schema_entry->value = g_new0(StatsSchemaValue, 1);
> +
> +    switch (pdesc->flags & KVM_STATS_TYPE_MASK) {
> +    case KVM_STATS_TYPE_CUMULATIVE:
> +        schema_entry->value->type = STATS_TYPE_CUMULATIVE;
> +        break;
> +    case KVM_STATS_TYPE_INSTANT:
> +        schema_entry->value->type = STATS_TYPE_INSTANT;
> +        break;
> +    case KVM_STATS_TYPE_PEAK:
> +        schema_entry->value->type = STATS_TYPE_PEAK;
> +        break;
> +    case KVM_STATS_TYPE_LINEAR_HIST:
> +        schema_entry->value->type = STATS_TYPE_LINEAR_HISTOGRAM;
> +        schema_entry->value->bucket_size = pdesc->bucket_size;
> +        schema_entry->value->has_bucket_size = true;
> +        break;
> +    case KVM_STATS_TYPE_LOG_HIST:
> +        schema_entry->value->type = STATS_TYPE_LOG2_HISTOGRAM;
> +        break;
> +    default:
> +        goto exit;
> +    }
> +
> +    switch (pdesc->flags & KVM_STATS_UNIT_MASK) {
> +    case KVM_STATS_UNIT_NONE:
> +        break;
> +    case KVM_STATS_UNIT_BYTES:
> +        schema_entry->value->has_unit = true;
> +        schema_entry->value->unit = STATS_UNIT_BYTES;
> +        break;
> +    case KVM_STATS_UNIT_CYCLES:
> +        schema_entry->value->has_unit = true;
> +        schema_entry->value->unit = STATS_UNIT_CYCLES;
> +        break;
> +    case KVM_STATS_UNIT_SECONDS:
> +        schema_entry->value->has_unit = true;
> +        schema_entry->value->unit = STATS_UNIT_SECONDS;
> +        break;
> +    default:
> +        goto exit;
> +    }
> +
> +    schema_entry->value->exponent = pdesc->exponent;
> +    if (pdesc->exponent) {
> +        switch (pdesc->flags & KVM_STATS_BASE_MASK) {
> +        case KVM_STATS_BASE_POW10:
> +            schema_entry->value->has_base = true;
> +            schema_entry->value->base = 10;
> +            break;
> +        case KVM_STATS_BASE_POW2:
> +            schema_entry->value->has_base = true;
> +            schema_entry->value->base = 2;
> +            break;
> +        default:
> +            goto exit;
> +        }
> +    }
> +
> +    schema_entry->value->name = g_strdup(pdesc->name);
> +    schema_entry->next = list;
> +    return schema_entry;
> +exit:
> +    g_free(schema_entry->value);
> +    g_free(schema_entry);
> +    return list;
> +}
> +
> +/* Cached stats descriptors */
> +typedef struct StatsDescriptors {
> +    char *ident; /* 'vm' or vCPU qom path */
> +    struct kvm_stats_desc *kvm_stats_desc;
> +    struct kvm_stats_header *kvm_stats_header;
> +    QTAILQ_ENTRY(StatsDescriptors) next;
> +} StatsDescriptors;
> +
> +static QTAILQ_HEAD(, StatsDescriptors) stats_descriptors =
> +    QTAILQ_HEAD_INITIALIZER(stats_descriptors);
> +
> +static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd,
> +                                                Error **errp)
> +{
> +    StatsDescriptors *descriptors;
> +    const char *ident;
> +    struct kvm_stats_desc *kvm_stats_desc;
> +    struct kvm_stats_header *kvm_stats_header;
> +    size_t size_desc;
> +    ssize_t ret;
> +
> +    switch (target) {
> +    case STATS_TARGET_VM:
> +        ident = StatsTarget_str(STATS_TARGET_VM);
> +        break;
> +    case STATS_TARGET_VCPU:
> +        ident = current_cpu->parent_obj.canonical_path;
> +        break;
> +    default:
> +        abort();
> +    }
> +
> +    QTAILQ_FOREACH(descriptors, &stats_descriptors, next) {
> +        if (g_str_equal(descriptors->ident, ident)) {
> +            return descriptors;
> +        }
> +    }
> +
> +    descriptors = g_new0(StatsDescriptors, 1);
> +
> +    /* Read stats header */
> +    kvm_stats_header = g_malloc(sizeof(*kvm_stats_header));
> +    ret = read(stats_fd, kvm_stats_header, sizeof(*kvm_stats_header));
> +    if (ret != sizeof(*kvm_stats_header)) {
> +        error_setg(errp, "KVM stats: failed to read stats header: "
> +                   "expected %zu actual %zu",
> +                   sizeof(*kvm_stats_header), ret);
> +        return NULL;
> +    }
> +    size_desc = sizeof(*kvm_stats_desc) + kvm_stats_header->name_size;
> +
> +    /* Read stats descriptors */
> +    kvm_stats_desc = g_malloc0_n(kvm_stats_header->num_desc, size_desc);
> +    ret = pread(stats_fd, kvm_stats_desc,
> +                size_desc * kvm_stats_header->num_desc,
> +                kvm_stats_header->desc_offset);
> +
> +    if (ret != size_desc * kvm_stats_header->num_desc) {
> +        error_setg(errp, "KVM stats: failed to read stats descriptors: "
> +                   "expected %zu actual %zu",
> +                   size_desc * kvm_stats_header->num_desc, ret);
> +        g_free(descriptors);

That's missing a free of kvm_stats_desc
(Sorry, I missed that last time)

> +        return NULL;
> +    }
> +    descriptors->kvm_stats_header = kvm_stats_header;
> +    descriptors->kvm_stats_desc = kvm_stats_desc;
> +    descriptors->ident = g_strdup(ident);

There's something that confuses me here; you check your set of
descriptors above to find any with the matching ident, and if you've
already got it you return it; OK.  Now, if you don't match then you
read some stats and store it with that ident - but I don't see
when you read the stats from the fd, what makes it read the stats that
correspond to 'ident' ?

> +    QTAILQ_INSERT_TAIL(&stats_descriptors, descriptors, next);
> +    return descriptors;
> +}
> +
> +static void query_stats(StatsResultList **result, StatsTarget target,
> +                        int stats_fd, Error **errp)
> +{
> +    struct kvm_stats_desc *kvm_stats_desc;
> +    struct kvm_stats_header *kvm_stats_header;
> +    StatsDescriptors *descriptors;
> +    g_autofree uint64_t *stats_data = NULL;
> +    struct kvm_stats_desc *pdesc;
> +    StatsList *stats_list = NULL;
> +    size_t size_desc, size_data = 0;
> +    ssize_t ret;
> +    int i;
> +
> +    descriptors = find_stats_descriptors(target, stats_fd, errp);
> +    if (!descriptors) {
> +        return;
> +    }
> +
> +    kvm_stats_header = descriptors->kvm_stats_header;
> +    kvm_stats_desc = descriptors->kvm_stats_desc;
> +    size_desc = sizeof(*kvm_stats_desc) + kvm_stats_header->name_size;
> +
> +    /* Tally the total data size; read schema data */
> +    for (i = 0; i < kvm_stats_header->num_desc; ++i) {
> +        pdesc = (void *)kvm_stats_desc + i * size_desc;
> +        size_data += pdesc->size * sizeof(*stats_data);
> +    }
> +
> +    stats_data = g_malloc0(size_data);
> +    ret = pread(stats_fd, stats_data, size_data, kvm_stats_header->data_offset);
> +
> +    if (ret != size_data) {
> +        error_setg(errp, "KVM stats: failed to read data: "
> +                   "expected %zu actual %zu", size_data, ret);
> +        return;
> +    }
> +
> +    for (i = 0; i < kvm_stats_header->num_desc; ++i) {
> +        uint64_t *stats;
> +        pdesc = (void *)kvm_stats_desc + i * size_desc;
> +
> +        /* Add entry to the list */
> +        stats = (void *)stats_data + pdesc->offset;
> +        stats_list = add_kvmstat_entry(pdesc, stats, stats_list, errp);
> +    }
> +
> +    if (!stats_list) {
> +        return;
> +    }
> +
> +    switch (target) {
> +    case STATS_TARGET_VM:
> +        add_stats_entry(result, STATS_PROVIDER_KVM, NULL, stats_list);
> +        break;
> +    case STATS_TARGET_VCPU:
> +        add_stats_entry(result, STATS_PROVIDER_KVM,
> +                        current_cpu->parent_obj.canonical_path,
> +                        stats_list);
> +        break;
> +    default:
> +        break;
> +    }
> +}
> +
> +static void query_stats_schema(StatsSchemaList **result, StatsTarget target,
> +                               int stats_fd, Error **errp)
> +{
> +    struct kvm_stats_desc *kvm_stats_desc;
> +    struct kvm_stats_header *kvm_stats_header;
> +    StatsDescriptors *descriptors;
> +    struct kvm_stats_desc *pdesc;
> +    StatsSchemaValueList *stats_list = NULL;
> +    size_t size_desc;
> +    int i;
> +
> +    descriptors = find_stats_descriptors(target, stats_fd, errp);
> +    if (!descriptors) {
> +        return;
> +    }
> +
> +    kvm_stats_header = descriptors->kvm_stats_header;
> +    kvm_stats_desc = descriptors->kvm_stats_desc;
> +    size_desc = sizeof(*kvm_stats_desc) + kvm_stats_header->name_size;
> +
> +    /* Tally the total data size; read schema data */
> +    for (i = 0; i < kvm_stats_header->num_desc; ++i) {
> +        pdesc = (void *)kvm_stats_desc + i * size_desc;
> +        stats_list = add_kvmschema_entry(pdesc, stats_list, errp);
> +    }
> +
> +    add_stats_schema(result, STATS_PROVIDER_KVM, target, stats_list);
> +}
> +
> +static void query_stats_vcpu(CPUState *cpu, run_on_cpu_data data)
> +{
> +    StatsArgs *kvm_stats_args = (StatsArgs *) data.host_ptr;
> +    int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL);
> +    Error *local_err = NULL;
> +
> +    if (stats_fd == -1) {
> +        error_setg_errno(&local_err, errno, "KVM stats: ioctl failed");
> +        error_propagate(kvm_stats_args->errp, local_err);
> +        return;
> +    }
> +    query_stats(kvm_stats_args->result.stats, STATS_TARGET_VCPU, stats_fd,
> +                kvm_stats_args->errp);
> +    close(stats_fd);
> +}
> +
> +static void query_stats_schema_vcpu(CPUState *cpu, run_on_cpu_data data)
> +{
> +    StatsArgs *kvm_stats_args = (StatsArgs *) data.host_ptr;
> +    int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL);
> +    Error *local_err = NULL;
> +
> +    if (stats_fd == -1) {
> +        error_setg_errno(&local_err, errno, "KVM stats: ioctl failed");
> +        error_propagate(kvm_stats_args->errp, local_err);
> +        return;
> +    }
> +    query_stats_schema(kvm_stats_args->result.schema, STATS_TARGET_VCPU, stats_fd,
> +                       kvm_stats_args->errp);
> +    close(stats_fd);
> +}
> +
> +static void query_stats_cb(StatsResultList **result, StatsTarget target, Error **errp)
> +{
> +    KVMState *s = kvm_state;
> +    CPUState *cpu;
> +    int stats_fd;
> +
> +    switch (target) {
> +    case STATS_TARGET_VM:
> +    {
> +        stats_fd = kvm_vm_ioctl(s, KVM_GET_STATS_FD, NULL);
> +        if (stats_fd == -1) {
> +            error_setg_errno(errp, errno, "KVM errno, stats: ioctl failed");
> +            return;
> +        }
> +        query_stats(result, target, stats_fd, errp);
> +        close(stats_fd);
> +        break;
> +    }
> +    case STATS_TARGET_VCPU:
> +    {
> +        StatsArgs stats_args;
> +        stats_args.result.stats = result;
> +        stats_args.errp = errp;
> +        CPU_FOREACH(cpu) {
> +            run_on_cpu(cpu, query_stats_vcpu, RUN_ON_CPU_HOST_PTR(&stats_args));
> +        }
> +        break;
> +    }
> +    default:
> +        break;
> +    }
> +}
> +
> +void query_stats_schemas_cb(StatsSchemaList **result, Error **errp)
> +{
> +    StatsArgs stats_args;
> +    KVMState *s = kvm_state;
> +    int stats_fd;
> +
> +    stats_fd = kvm_vm_ioctl(s, KVM_GET_STATS_FD, NULL);
> +    if (stats_fd == -1) {
> +        error_setg(errp, "KVM stats: ioctl failed");

missed an _errno

> +        return;
> +    }
> +    query_stats_schema(result, STATS_TARGET_VM, stats_fd, errp);
> +    close(stats_fd);
> +
> +    stats_args.result.schema = result;
> +    stats_args.errp = errp;
> +    run_on_cpu(first_cpu, query_stats_schema_vcpu, RUN_ON_CPU_HOST_PTR(&stats_args));
> +}
> diff --git a/qapi/stats.json b/qapi/stats.json
> index ada0fbf26f..df7c4d886c 100644
> --- a/qapi/stats.json
> +++ b/qapi/stats.json
> @@ -52,7 +52,7 @@
>  # Since: 7.1
>  ##
>  { 'enum': 'StatsProvider',
> -  'data': [ ] }
> +  'data': [ 'kvm' ] }
>  
>  ##
>  # @StatsTarget:
> -- 
> 2.36.1
> 
>

On 6/7/22 19:44, Dr. David Alan Gilbert wrote:

>> +        return NULL;
>> +    }
>> +    descriptors->kvm_stats_header = kvm_stats_header;
>> +    descriptors->kvm_stats_desc = kvm_stats_desc;
>> +    descriptors->ident = g_strdup(ident);
> 
> There's something that confuses me here; you check your set of
> descriptors above to find any with the matching ident, and if you've
> already got it you return it; OK.  Now, if you don't match then you
> read some stats and store it with that ident - but I don't see
> when you read the stats from the fd, what makes it read the stats that
> correspond to 'ident' ?

If you mean why not some other source, each source has a different file 
descriptor:

+    int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL);

but the descriptors are consistent every time KVM_GET_STATS_FD is 
called, so basically "ident" can be used as a cache key.

If you mean how does it access the right stat, here it uses the offset
field in the descriptor

     ret = pread(stats_fd, stats_data, size_data, 
kvm_stats_header->data_offset);
     ...
     for (i = 0; i < kvm_stats_header->num_desc; ++i) {
         uint64_t *stats;
         pdesc = (void *)kvm_stats_desc + i * size_desc;

         /* Add entry to the list */
         stats = (void *)stats_data + pdesc->offset;

Paolo

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> On 6/7/22 19:44, Dr. David Alan Gilbert wrote:
> 
> > > +        return NULL;
> > > +    }
> > > +    descriptors->kvm_stats_header = kvm_stats_header;
> > > +    descriptors->kvm_stats_desc = kvm_stats_desc;
> > > +    descriptors->ident = g_strdup(ident);
> > 
> > There's something that confuses me here; you check your set of
> > descriptors above to find any with the matching ident, and if you've
> > already got it you return it; OK.  Now, if you don't match then you
> > read some stats and store it with that ident - but I don't see
> > when you read the stats from the fd, what makes it read the stats that
> > correspond to 'ident' ?
> 
> If you mean why not some other source, each source has a different file
> descriptor:
> 
> +    int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL);
> 
> but the descriptors are consistent every time KVM_GET_STATS_FD is called, so
> basically "ident" can be used as a cache key.

Ah OK, this is what I was after; it's a little weird that the caller
does the ioctl to get the stats-fd, but it does the lookup internally
with current_cpu for the ident.

Some comments would help!

Dave

> If you mean how does it access the right stat, here it uses the offset
> field in the descriptor
> 
>     ret = pread(stats_fd, stats_data, size_data,
> kvm_stats_header->data_offset);
>     ...
>     for (i = 0; i < kvm_stats_header->num_desc; ++i) {
>         uint64_t *stats;
>         pdesc = (void *)kvm_stats_desc + i * size_desc;
> 
>         /* Add entry to the list */
>         stats = (void *)stats_data + pdesc->offset;
> 
> Paolo
>

On 6/8/22 16:52, Dr. David Alan Gilbert wrote:
>> If you mean why not some other source, each source has a different file
>> descriptor:
>>
>> +    int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL);
>>
>> but the descriptors are consistent every time KVM_GET_STATS_FD is called, so
>> basically "ident" can be used as a cache key.
>
> Ah OK, this is what I was after; it's a little weird that the caller
> does the ioctl to get the stats-fd, but it does the lookup internally
> with current_cpu for the ident.

Oh yeah that's weird.

Let me squash in this:

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 023bf4ea79..71896ad173 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -3871,17 +3871,7 @@ static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd
      size_t size_desc;
      ssize_t ret;
  
-    switch (target) {
-    case STATS_TARGET_VM:
-        ident = StatsTarget_str(STATS_TARGET_VM);
-        break;
-    case STATS_TARGET_VCPU:
-        ident = current_cpu->parent_obj.canonical_path;
-        break;
-    default:
-        abort();
-    }
-
+    ident = StatsTarget_str(target);
      QTAILQ_FOREACH(descriptors, &stats_descriptors, next) {
          if (g_str_equal(descriptors->ident, ident)) {
              return descriptors;
@@ -3917,7 +3907,7 @@ static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd
      }
      descriptors->kvm_stats_header = kvm_stats_header;
      descriptors->kvm_stats_desc = kvm_stats_desc;
-    descriptors->ident = g_strdup(ident);
+    descriptors->ident = ident;
      QTAILQ_INSERT_TAIL(&stats_descriptors, descriptors, next);
      return descriptors;
  }

(once I test it).

Paolo

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> On 6/8/22 16:52, Dr. David Alan Gilbert wrote:
> > > If you mean why not some other source, each source has a different file
> > > descriptor:
> > > 
> > > +    int stats_fd = kvm_vcpu_ioctl(cpu, KVM_GET_STATS_FD, NULL);
> > > 
> > > but the descriptors are consistent every time KVM_GET_STATS_FD is called, so
> > > basically "ident" can be used as a cache key.
> > 
> > Ah OK, this is what I was after; it's a little weird that the caller
> > does the ioctl to get the stats-fd, but it does the lookup internally
> > with current_cpu for the ident.
> 
> Oh yeah that's weird.
> 
> Let me squash in this:

Yeh that's nicer; a comment something like:

'Find descriptors for 'target', either that have already been read or
 query 'stats_fd' to read them from kvm'

?

Dave

> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 023bf4ea79..71896ad173 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -3871,17 +3871,7 @@ static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd
>      size_t size_desc;
>      ssize_t ret;
> -    switch (target) {
> -    case STATS_TARGET_VM:
> -        ident = StatsTarget_str(STATS_TARGET_VM);
> -        break;
> -    case STATS_TARGET_VCPU:
> -        ident = current_cpu->parent_obj.canonical_path;
> -        break;
> -    default:
> -        abort();
> -    }
> -
> +    ident = StatsTarget_str(target);
>      QTAILQ_FOREACH(descriptors, &stats_descriptors, next) {
>          if (g_str_equal(descriptors->ident, ident)) {
>              return descriptors;
> @@ -3917,7 +3907,7 @@ static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd
>      }
>      descriptors->kvm_stats_header = kvm_stats_header;
>      descriptors->kvm_stats_desc = kvm_stats_desc;
> -    descriptors->ident = g_strdup(ident);
> +    descriptors->ident = ident;
>      QTAILQ_INSERT_TAIL(&stats_descriptors, descriptors, next);
>      return descriptors;
>  }
> 
> (once I test it).
> 
> Paolo
>

On 6/8/22 18:01, Dr. David Alan Gilbert wrote:
> 'Find descriptors for 'target', either that have already been read or
>   query 'stats_fd' to read them from kvm'

/*
  * Return the descriptors for 'target', that either have already been
  * read or are retrieved from 'stats_fd'.
  */

Paolo

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> On 6/8/22 18:01, Dr. David Alan Gilbert wrote:
> > 'Find descriptors for 'target', either that have already been read or
> >   query 'stats_fd' to read them from kvm'
> 
> /*
>  * Return the descriptors for 'target', that either have already been
>  * read or are retrieved from 'stats_fd'.
>  */


Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> Paolo
>