Re: [PATCH] kvm: Detect number of available memory slots from the host kernel

[Gleb Natapov <gleb@redhat.com>]

On Fri, Dec 07, 2012 at 12:46:10PM -0700, Alex Williamson wrote:
> The kernel already exposes an interface for this, x86 returns a proper
> value and for the rest we can default to the defacto standard of 32.
> The primary motivation for this is to support more PCI assigned
> devices, both through pci-assign and vfio-pci.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
>  kvm-all.c |   27 ++++++++++++++++++---------
>  1 file changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/kvm-all.c b/kvm-all.c
> index 8e9a8d8..34d97f3 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -71,7 +71,8 @@ typedef struct kvm_dirty_log KVMDirtyLog;
>  
>  struct KVMState
>  {
> -    KVMSlot slots[32];
> +    KVMSlot *slots;
> +    int num_slots;
>      int fd;
>      int vmfd;
>      int coalesced_mmio;
> @@ -120,7 +121,7 @@ static KVMSlot *kvm_alloc_slot(KVMState *s)
>  {
>      int i;
>  
> -    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
> +    for (i = 0; i < s->num_slots; i++) {
>          if (s->slots[i].memory_size == 0) {
>              return &s->slots[i];
>          }
> @@ -136,7 +137,7 @@ static KVMSlot *kvm_lookup_matching_slot(KVMState *s,
>  {
>      int i;
>  
> -    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
> +    for (i = 0; i < s->num_slots; i++) {
>          KVMSlot *mem = &s->slots[i];
>  
>          if (start_addr == mem->start_addr &&
> @@ -158,7 +159,7 @@ static KVMSlot *kvm_lookup_overlapping_slot(KVMState *s,
>      KVMSlot *found = NULL;
>      int i;
>  
> -    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
> +    for (i = 0; i < s->num_slots; i++) {
>          KVMSlot *mem = &s->slots[i];
>  
>          if (mem->memory_size == 0 ||
> @@ -180,7 +181,7 @@ int kvm_physical_memory_addr_from_host(KVMState *s, void *ram,
>  {
>      int i;
>  
> -    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
> +    for (i = 0; i < s->num_slots; i++) {
>          KVMSlot *mem = &s->slots[i];
>  
>          if (ram >= mem->ram && ram < mem->ram + mem->memory_size) {
> @@ -340,7 +341,7 @@ static int kvm_set_migration_log(int enable)
>  
>      s->migration_log = enable;
>  
> -    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
> +    for (i = 0; i < s->num_slots; i++) {
>          mem = &s->slots[i];
>  
>          if (!mem->memory_size) {
> @@ -1268,9 +1269,6 @@ int kvm_init(void)
>  #ifdef KVM_CAP_SET_GUEST_DEBUG
>      QTAILQ_INIT(&s->kvm_sw_breakpoints);
>  #endif
> -    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
> -        s->slots[i].slot = i;
> -    }
>      s->vmfd = -1;
>      s->fd = qemu_open("/dev/kvm", O_RDWR);
>      if (s->fd == -1) {
> @@ -1324,6 +1322,16 @@ int kvm_init(void)
>          goto err;
>      }
>  
> +    s->num_slots = kvm_check_extension(s, KVM_CAP_NR_MEMSLOTS);
> +    if (s->num_slots <= 0) {
kvm_check_extension() never returns negative value, so !s->num_slots
check is enough. Other than that minor nit looks OK.
 
> +        s->num_slots = 32;
> +    }
> +    s->slots = g_malloc0(s->num_slots * sizeof(*s->slots));
> +
> +    for (i = 0; i < s->num_slots; i++) {
> +        s->slots[i].slot = i;
> +    }
> +
>      s->coalesced_mmio = kvm_check_extension(s, KVM_CAP_COALESCED_MMIO);
>  
>      s->broken_set_mem_region = 1;
> @@ -1393,6 +1401,7 @@ err:
>      if (s->fd != -1) {
>          close(s->fd);
>      }
> +    g_free(s->slots);
>      g_free(s);
>  
>      return ret;

--
			Gleb.