[Qemu-devel] [PATCH v3 0/2] error-report: introduce {error|warn}_report_once

[Qemu-devel] [PATCH v3 0/2] error-report: introduce {error|warn}_report_once

[Peter Xu]

v3:
- reindent in patch 2, dump more things [Philippe]

v2:
- for patch 1: replace tabs, add trivial comment [Markus]
  (I didn't add much comment otherwise I'll need to duplicate what's
   there in error_report())
- add patch 2

Patch 1 introduce the helpers.

Patch 2 use it to replace VT-d trace_vtd_err().

Please review.  Thanks.

Peter Xu (2):
  qemu-error: introduce {error|warn}_report_once
  intel-iommu: start to use error_report_once

 include/qemu/error-report.h | 26 ++++++++++++++++
 hw/i386/intel_iommu.c       | 59 +++++++++++++++++++++----------------
 hw/i386/trace-events        |  1 -
 3 files changed, 59 insertions(+), 27 deletions(-)

-- 
2.17.0

[Qemu-devel] [PATCH v3 1/2] qemu-error: introduce {error|warn}_report_once

[Peter Xu]

I stole the printk_once() macro.

I always wanted to be able to print some error directly if there is a
buffer to dump, however we can't use error_report() where the code path
can be triggered by DDOS attack.  To avoid that, we can introduce a
print-once-like function for it.  Meanwhile, we also introduce the
corresponding helper for warn_report().

CC: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/qemu/error-report.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/qemu/error-report.h b/include/qemu/error-report.h
index e1c8ae1a52..3e6e84801f 100644
--- a/include/qemu/error-report.h
+++ b/include/qemu/error-report.h
@@ -44,6 +44,32 @@ void error_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 void warn_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 void info_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 
+/* Similar to error_report(), but it only prints the message once. */
+#define error_report_once(fmt, ...)             \
+    ({                                          \
+        static bool __print_once;               \
+        bool __ret_print_once = !__print_once;  \
+                                                \
+        if (!__print_once) {                    \
+            __print_once = true;                \
+            error_report(fmt, ##__VA_ARGS__);   \
+        }                                       \
+        unlikely(__ret_print_once);             \
+    })
+
+/* Similar to warn_report(), but it only prints the message once. */
+#define warn_report_once(fmt, ...)              \
+    ({                                          \
+        static bool __print_once;               \
+        bool __ret_print_once = !__print_once;  \
+                                                \
+        if (!__print_once) {                    \
+            __print_once = true;                \
+            warn_report(fmt, ##__VA_ARGS__);   \
+        }                                       \
+        unlikely(__ret_print_once);             \
+    })
+
 const char *error_get_progname(void);
 extern bool enable_timestamp_msg;
 
-- 
2.17.0

[Qemu-devel] [PATCH v3 2/2] intel-iommu: start to use error_report_once

[Peter Xu]

Replace existing trace_vtd_err() with error_report_once() then stderr
will capture something if any of the error happens, meanwhile we don't
suffer from any DDOS.  Then remove the trace point.  Since at it,
provide more information where proper (now we can pass parameters into
the report function).

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 hw/i386/intel_iommu.c | 59 ++++++++++++++++++++++++-------------------
 hw/i386/trace-events  |  1 -
 2 files changed, 33 insertions(+), 27 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index fb31de9416..fa6df921ee 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -285,14 +285,14 @@ static void vtd_generate_fault_event(IntelIOMMUState *s, uint32_t pre_fsts)
 {
     if (pre_fsts & VTD_FSTS_PPF || pre_fsts & VTD_FSTS_PFO ||
         pre_fsts & VTD_FSTS_IQE) {
-        trace_vtd_err("There are previous interrupt conditions "
-                      "to be serviced by software, fault event "
-                      "is not generated.");
+        error_report_once("There are previous interrupt conditions "
+                          "to be serviced by software, fault event "
+                          "is not generated");
         return;
     }
     vtd_set_clear_mask_long(s, DMAR_FECTL_REG, 0, VTD_FECTL_IP);
     if (vtd_get_long_raw(s, DMAR_FECTL_REG) & VTD_FECTL_IM) {
-        trace_vtd_err("Interrupt Mask set, irq is not generated.");
+        error_report_once("Interrupt Mask set, irq is not generated");
     } else {
         vtd_generate_interrupt(s, DMAR_FEADDR_REG, DMAR_FEDATA_REG);
         vtd_set_clear_mask_long(s, DMAR_FECTL_REG, VTD_FECTL_IP, 0);
@@ -400,20 +400,20 @@ static void vtd_report_dmar_fault(IntelIOMMUState *s, uint16_t source_id,
     trace_vtd_dmar_fault(source_id, fault, addr, is_write);
 
     if (fsts_reg & VTD_FSTS_PFO) {
-        trace_vtd_err("New fault is not recorded due to "
-                      "Primary Fault Overflow.");
+        error_report_once("New fault is not recorded due to "
+                          "Primary Fault Overflow");
         return;
     }
 
     if (vtd_try_collapse_fault(s, source_id)) {
-        trace_vtd_err("New fault is not recorded due to "
-                      "compression of faults.");
+        error_report_once("New fault is not recorded due to "
+                          "compression of faults");
         return;
     }
 
     if (vtd_is_frcd_set(s, s->next_frcd_reg)) {
-        trace_vtd_err("Next Fault Recording Reg is used, "
-                      "new fault is not recorded, set PFO field.");
+        error_report_once("Next Fault Recording Reg is used, "
+                          "new fault is not recorded, set PFO field");
         vtd_set_clear_mask_long(s, DMAR_FSTS_REG, 0, VTD_FSTS_PFO);
         return;
     }
@@ -421,8 +421,8 @@ static void vtd_report_dmar_fault(IntelIOMMUState *s, uint16_t source_id,
     vtd_record_frcd(s, s->next_frcd_reg, source_id, addr, fault, is_write);
 
     if (fsts_reg & VTD_FSTS_PPF) {
-        trace_vtd_err("There are pending faults already, "
-                      "fault event is not generated.");
+        error_report_once("There are pending faults already, "
+                          "fault event is not generated");
         vtd_set_frcd_and_update_ppf(s, s->next_frcd_reg);
         s->next_frcd_reg++;
         if (s->next_frcd_reg == DMAR_FRCD_REG_NR) {
@@ -1339,7 +1339,8 @@ static uint64_t vtd_context_cache_invalidate(IntelIOMMUState *s, uint64_t val)
         break;
 
     default:
-        trace_vtd_err("Context cache invalidate type error.");
+        error_report_once("%s: invalid context: 0x%"PRIx64,
+                          __func__, val);
         caig = 0;
     }
     return caig;
@@ -1445,7 +1446,8 @@ static uint64_t vtd_iotlb_flush(IntelIOMMUState *s, uint64_t val)
         am = VTD_IVA_AM(addr);
         addr = VTD_IVA_ADDR(addr);
         if (am > VTD_MAMV) {
-            trace_vtd_err("IOTLB PSI flush: address mask overflow.");
+            error_report_once("%s: address mask overflow: 0x%"PRIx64,
+                              __func__, vtd_get_quad_raw(s, DMAR_IVA_REG));
             iaig = 0;
             break;
         }
@@ -1454,7 +1456,8 @@ static uint64_t vtd_iotlb_flush(IntelIOMMUState *s, uint64_t val)
         break;
 
     default:
-        trace_vtd_err("IOTLB flush: invalid granularity.");
+        error_report_once("%s: invalid granularity: 0x%"PRIx64,
+                          __func__, val);
         iaig = 0;
     }
     return iaig;
@@ -1604,8 +1607,8 @@ static void vtd_handle_ccmd_write(IntelIOMMUState *s)
     /* Context-cache invalidation request */
     if (val & VTD_CCMD_ICC) {
         if (s->qi_enabled) {
-            trace_vtd_err("Queued Invalidation enabled, "
-                          "should not use register-based invalidation");
+            error_report_once("Queued Invalidation enabled, "
+                              "should not use register-based invalidation");
             return;
         }
         ret = vtd_context_cache_invalidate(s, val);
@@ -1625,8 +1628,8 @@ static void vtd_handle_iotlb_write(IntelIOMMUState *s)
     /* IOTLB invalidation request */
     if (val & VTD_TLB_IVT) {
         if (s->qi_enabled) {
-            trace_vtd_err("Queued Invalidation enabled, "
-                          "should not use register-based invalidation.");
+            error_report_once("Queued Invalidation enabled, "
+                              "should not use register-based invalidation");
             return;
         }
         ret = vtd_iotlb_flush(s, val);
@@ -1644,7 +1647,7 @@ static bool vtd_get_inv_desc(dma_addr_t base_addr, uint32_t offset,
     dma_addr_t addr = base_addr + offset * sizeof(*inv_desc);
     if (dma_memory_read(&address_space_memory, addr, inv_desc,
         sizeof(*inv_desc))) {
-        trace_vtd_err("Read INV DESC failed.");
+        error_report_once("Read INV DESC failed");
         inv_desc->lo = 0;
         inv_desc->hi = 0;
         return false;
@@ -1999,7 +2002,8 @@ static uint64_t vtd_mem_read(void *opaque, hwaddr addr, unsigned size)
     trace_vtd_reg_read(addr, size);
 
     if (addr + size > DMAR_REG_SIZE) {
-        trace_vtd_err("Read MMIO over range.");
+        error_report_once("%s: MMIO over range: addr=0x%"PRIx64
+                          " size=0x%u", __func__, addr, size);
         return (uint64_t)-1;
     }
 
@@ -2050,7 +2054,8 @@ static void vtd_mem_write(void *opaque, hwaddr addr,
     trace_vtd_reg_write(addr, size, val);
 
     if (addr + size > DMAR_REG_SIZE) {
-        trace_vtd_err("Write MMIO over range.");
+        error_report_once("%s: MMIO over range: addr=0x%"PRIx64
+                          " size=0x%u", __func__, addr, size);
         return;
     }
 
@@ -2432,7 +2437,8 @@ static int vtd_irte_get(IntelIOMMUState *iommu, uint16_t index,
     addr = iommu->intr_root + index * sizeof(*entry);
     if (dma_memory_read(&address_space_memory, addr, entry,
                         sizeof(*entry))) {
-        trace_vtd_err("Memory read failed for IRTE.");
+        error_report_once("%s: read failed: ind=0x%"PRIu16
+                          " addr=0x%"PRIx64, __func__, index, addr);
         return -VTD_FR_IR_ROOT_INVAL;
     }
 
@@ -2564,14 +2570,15 @@ static int vtd_interrupt_remap_msi(IntelIOMMUState *iommu,
     }
 
     if (origin->address & VTD_MSI_ADDR_HI_MASK) {
-        trace_vtd_err("MSI address high 32 bits non-zero when "
-                      "Interrupt Remapping enabled.");
+        error_report_once("%s: MSI address high 32 bits non-zero detected: "
+                          "address=0x%"PRIx64, __func__, origin->address);
         return -VTD_FR_IR_REQ_RSVD;
     }
 
     addr.data = origin->address & VTD_MSI_ADDR_LO_MASK;
     if (addr.addr.__head != 0xfee) {
-        trace_vtd_err("MSI addr low 32 bit invalid.");
+        error_report_once("%s: MSI address low 32 bit invalid: 0x%"PRIx32,
+                          __func__, addr.data);
         return -VTD_FR_IR_REQ_RSVD;
     }
 
diff --git a/hw/i386/trace-events b/hw/i386/trace-events
index 22d44648af..e08cf2a9a7 100644
--- a/hw/i386/trace-events
+++ b/hw/i386/trace-events
@@ -68,7 +68,6 @@ vtd_ir_remap_msi_req(uint64_t addr, uint64_t data) "addr 0x%"PRIx64" data 0x%"PR
 vtd_fsts_ppf(bool set) "FSTS PPF bit set to %d"
 vtd_fsts_clear_ip(void) ""
 vtd_frr_new(int index, uint64_t hi, uint64_t lo) "index %d high 0x%"PRIx64" low 0x%"PRIx64
-vtd_err(const char *str) "%s"
 vtd_err_dmar_iova_overflow(uint64_t iova) "iova 0x%"PRIx64
 vtd_err_dmar_slpte_read_error(uint64_t iova, int level) "iova 0x%"PRIx64" level %d"
 vtd_err_dmar_slpte_perm_error(uint64_t iova, int level, uint64_t slpte, bool is_write) "iova 0x%"PRIx64" level %d slpte 0x%"PRIx64" write %d"
-- 
2.17.0

Re: [Qemu-devel] [PATCH v3 2/2] intel-iommu: start to use error_report_once

[Philippe Mathieu-Daudé]

On 05/23/2018 12:18 AM, Peter Xu wrote:
> Replace existing trace_vtd_err() with error_report_once() then stderr
> will capture something if any of the error happens, meanwhile we don't
> suffer from any DDOS.  Then remove the trace point.  Since at it,
> provide more information where proper (now we can pass parameters into
> the report function).
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

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

> ---
>  hw/i386/intel_iommu.c | 59 ++++++++++++++++++++++++-------------------
>  hw/i386/trace-events  |  1 -
>  2 files changed, 33 insertions(+), 27 deletions(-)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index fb31de9416..fa6df921ee 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -285,14 +285,14 @@ static void vtd_generate_fault_event(IntelIOMMUState *s, uint32_t pre_fsts)
>  {
>      if (pre_fsts & VTD_FSTS_PPF || pre_fsts & VTD_FSTS_PFO ||
>          pre_fsts & VTD_FSTS_IQE) {
> -        trace_vtd_err("There are previous interrupt conditions "
> -                      "to be serviced by software, fault event "
> -                      "is not generated.");
> +        error_report_once("There are previous interrupt conditions "
> +                          "to be serviced by software, fault event "
> +                          "is not generated");
>          return;
>      }
>      vtd_set_clear_mask_long(s, DMAR_FECTL_REG, 0, VTD_FECTL_IP);
>      if (vtd_get_long_raw(s, DMAR_FECTL_REG) & VTD_FECTL_IM) {
> -        trace_vtd_err("Interrupt Mask set, irq is not generated.");
> +        error_report_once("Interrupt Mask set, irq is not generated");
>      } else {
>          vtd_generate_interrupt(s, DMAR_FEADDR_REG, DMAR_FEDATA_REG);
>          vtd_set_clear_mask_long(s, DMAR_FECTL_REG, VTD_FECTL_IP, 0);
> @@ -400,20 +400,20 @@ static void vtd_report_dmar_fault(IntelIOMMUState *s, uint16_t source_id,
>      trace_vtd_dmar_fault(source_id, fault, addr, is_write);
>  
>      if (fsts_reg & VTD_FSTS_PFO) {
> -        trace_vtd_err("New fault is not recorded due to "
> -                      "Primary Fault Overflow.");
> +        error_report_once("New fault is not recorded due to "
> +                          "Primary Fault Overflow");
>          return;
>      }
>  
>      if (vtd_try_collapse_fault(s, source_id)) {
> -        trace_vtd_err("New fault is not recorded due to "
> -                      "compression of faults.");
> +        error_report_once("New fault is not recorded due to "
> +                          "compression of faults");
>          return;
>      }
>  
>      if (vtd_is_frcd_set(s, s->next_frcd_reg)) {
> -        trace_vtd_err("Next Fault Recording Reg is used, "
> -                      "new fault is not recorded, set PFO field.");
> +        error_report_once("Next Fault Recording Reg is used, "
> +                          "new fault is not recorded, set PFO field");
>          vtd_set_clear_mask_long(s, DMAR_FSTS_REG, 0, VTD_FSTS_PFO);
>          return;
>      }
> @@ -421,8 +421,8 @@ static void vtd_report_dmar_fault(IntelIOMMUState *s, uint16_t source_id,
>      vtd_record_frcd(s, s->next_frcd_reg, source_id, addr, fault, is_write);
>  
>      if (fsts_reg & VTD_FSTS_PPF) {
> -        trace_vtd_err("There are pending faults already, "
> -                      "fault event is not generated.");
> +        error_report_once("There are pending faults already, "
> +                          "fault event is not generated");
>          vtd_set_frcd_and_update_ppf(s, s->next_frcd_reg);
>          s->next_frcd_reg++;
>          if (s->next_frcd_reg == DMAR_FRCD_REG_NR) {
> @@ -1339,7 +1339,8 @@ static uint64_t vtd_context_cache_invalidate(IntelIOMMUState *s, uint64_t val)
>          break;
>  
>      default:
> -        trace_vtd_err("Context cache invalidate type error.");
> +        error_report_once("%s: invalid context: 0x%"PRIx64,
> +                          __func__, val);
>          caig = 0;
>      }
>      return caig;
> @@ -1445,7 +1446,8 @@ static uint64_t vtd_iotlb_flush(IntelIOMMUState *s, uint64_t val)
>          am = VTD_IVA_AM(addr);
>          addr = VTD_IVA_ADDR(addr);
>          if (am > VTD_MAMV) {
> -            trace_vtd_err("IOTLB PSI flush: address mask overflow.");
> +            error_report_once("%s: address mask overflow: 0x%"PRIx64,
> +                              __func__, vtd_get_quad_raw(s, DMAR_IVA_REG));
>              iaig = 0;
>              break;
>          }
> @@ -1454,7 +1456,8 @@ static uint64_t vtd_iotlb_flush(IntelIOMMUState *s, uint64_t val)
>          break;
>  
>      default:
> -        trace_vtd_err("IOTLB flush: invalid granularity.");
> +        error_report_once("%s: invalid granularity: 0x%"PRIx64,
> +                          __func__, val);
>          iaig = 0;
>      }
>      return iaig;
> @@ -1604,8 +1607,8 @@ static void vtd_handle_ccmd_write(IntelIOMMUState *s)
>      /* Context-cache invalidation request */
>      if (val & VTD_CCMD_ICC) {
>          if (s->qi_enabled) {
> -            trace_vtd_err("Queued Invalidation enabled, "
> -                          "should not use register-based invalidation");
> +            error_report_once("Queued Invalidation enabled, "
> +                              "should not use register-based invalidation");
>              return;
>          }
>          ret = vtd_context_cache_invalidate(s, val);
> @@ -1625,8 +1628,8 @@ static void vtd_handle_iotlb_write(IntelIOMMUState *s)
>      /* IOTLB invalidation request */
>      if (val & VTD_TLB_IVT) {
>          if (s->qi_enabled) {
> -            trace_vtd_err("Queued Invalidation enabled, "
> -                          "should not use register-based invalidation.");
> +            error_report_once("Queued Invalidation enabled, "
> +                              "should not use register-based invalidation");
>              return;
>          }
>          ret = vtd_iotlb_flush(s, val);
> @@ -1644,7 +1647,7 @@ static bool vtd_get_inv_desc(dma_addr_t base_addr, uint32_t offset,
>      dma_addr_t addr = base_addr + offset * sizeof(*inv_desc);
>      if (dma_memory_read(&address_space_memory, addr, inv_desc,
>          sizeof(*inv_desc))) {
> -        trace_vtd_err("Read INV DESC failed.");
> +        error_report_once("Read INV DESC failed");
>          inv_desc->lo = 0;
>          inv_desc->hi = 0;
>          return false;
> @@ -1999,7 +2002,8 @@ static uint64_t vtd_mem_read(void *opaque, hwaddr addr, unsigned size)
>      trace_vtd_reg_read(addr, size);
>  
>      if (addr + size > DMAR_REG_SIZE) {
> -        trace_vtd_err("Read MMIO over range.");
> +        error_report_once("%s: MMIO over range: addr=0x%"PRIx64
> +                          " size=0x%u", __func__, addr, size);
>          return (uint64_t)-1;
>      }
>  
> @@ -2050,7 +2054,8 @@ static void vtd_mem_write(void *opaque, hwaddr addr,
>      trace_vtd_reg_write(addr, size, val);
>  
>      if (addr + size > DMAR_REG_SIZE) {
> -        trace_vtd_err("Write MMIO over range.");
> +        error_report_once("%s: MMIO over range: addr=0x%"PRIx64
> +                          " size=0x%u", __func__, addr, size);
>          return;
>      }
>  
> @@ -2432,7 +2437,8 @@ static int vtd_irte_get(IntelIOMMUState *iommu, uint16_t index,
>      addr = iommu->intr_root + index * sizeof(*entry);
>      if (dma_memory_read(&address_space_memory, addr, entry,
>                          sizeof(*entry))) {
> -        trace_vtd_err("Memory read failed for IRTE.");
> +        error_report_once("%s: read failed: ind=0x%"PRIu16
> +                          " addr=0x%"PRIx64, __func__, index, addr);
>          return -VTD_FR_IR_ROOT_INVAL;
>      }
>  
> @@ -2564,14 +2570,15 @@ static int vtd_interrupt_remap_msi(IntelIOMMUState *iommu,
>      }
>  
>      if (origin->address & VTD_MSI_ADDR_HI_MASK) {
> -        trace_vtd_err("MSI address high 32 bits non-zero when "
> -                      "Interrupt Remapping enabled.");
> +        error_report_once("%s: MSI address high 32 bits non-zero detected: "
> +                          "address=0x%"PRIx64, __func__, origin->address);
>          return -VTD_FR_IR_REQ_RSVD;
>      }
>  
>      addr.data = origin->address & VTD_MSI_ADDR_LO_MASK;
>      if (addr.addr.__head != 0xfee) {
> -        trace_vtd_err("MSI addr low 32 bit invalid.");
> +        error_report_once("%s: MSI address low 32 bit invalid: 0x%"PRIx32,
> +                          __func__, addr.data);
>          return -VTD_FR_IR_REQ_RSVD;
>      }
>  
> diff --git a/hw/i386/trace-events b/hw/i386/trace-events
> index 22d44648af..e08cf2a9a7 100644
> --- a/hw/i386/trace-events
> +++ b/hw/i386/trace-events
> @@ -68,7 +68,6 @@ vtd_ir_remap_msi_req(uint64_t addr, uint64_t data) "addr 0x%"PRIx64" data 0x%"PR
>  vtd_fsts_ppf(bool set) "FSTS PPF bit set to %d"
>  vtd_fsts_clear_ip(void) ""
>  vtd_frr_new(int index, uint64_t hi, uint64_t lo) "index %d high 0x%"PRIx64" low 0x%"PRIx64
> -vtd_err(const char *str) "%s"
>  vtd_err_dmar_iova_overflow(uint64_t iova) "iova 0x%"PRIx64
>  vtd_err_dmar_slpte_read_error(uint64_t iova, int level) "iova 0x%"PRIx64" level %d"
>  vtd_err_dmar_slpte_perm_error(uint64_t iova, int level, uint64_t slpte, bool is_write) "iova 0x%"PRIx64" level %d slpte 0x%"PRIx64" write %d"
> 

Re: [Qemu-devel] [PATCH v3 1/2] qemu-error: introduce {error|warn}_report_once

[Eric Blake]

On 05/22/2018 10:18 PM, Peter Xu wrote:
> I stole the printk_once() macro.
> 
> I always wanted to be able to print some error directly if there is a
> buffer to dump, however we can't use error_report() where the code path
> can be triggered by DDOS attack.  To avoid that, we can introduce a
> print-once-like function for it.  Meanwhile, we also introduce the
> corresponding helper for warn_report().
> 
> CC: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>   include/qemu/error-report.h | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
> 
> diff --git a/include/qemu/error-report.h b/include/qemu/error-report.h
> index e1c8ae1a52..3e6e84801f 100644
> --- a/include/qemu/error-report.h
> +++ b/include/qemu/error-report.h
> @@ -44,6 +44,32 @@ void error_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
>   void warn_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
>   void info_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
>   
> +/* Similar to error_report(), but it only prints the message once. */
> +#define error_report_once(fmt, ...)             \
> +    ({                                          \
> +        static bool __print_once;               \
> +        bool __ret_print_once = !__print_once;  \

In v1 you were asked to avoid leading double underscore 
(https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg03442.html; 
use things like 'print_once_' instead) and to document the return value 
of these macros 
(https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg03503.html; 
having the return value makes it possible to write conditional code that 
caches further information about a first, but not repeat, failures). 
Why hasn't that happened?

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