[PATCH] dump: enhance win_dump_available to report properly

[Nikolai Barybin <nikolai.barybin@virtuozzo.com>]

QMP query-dump-guest-memory-capability reports win dump as available for
any x86 VM, which is false.

This patch implements proper query of vmcoreinfo and calculation of
guest note size. Based on that we can surely report whether win dump
available or not.

For further reference one may review this libvirt discussion:
https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/HJ3JRLWLGN3IKIC22OQ3PMZ4J3EFG5XB/#HJ3JRLWLGN3IKIC22OQ3PMZ4J3EFG5XB
[PATCH 0/4] Allow xml-configured coredump format on VM crash

Signed-off-by: Nikolai Barybin <nikolai.barybin@virtuozzo.com>
---
 dump/win_dump.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/dump/win_dump.c b/dump/win_dump.c
index 3162e8bd48..4bb1b28e63 100644
--- a/dump/win_dump.c
+++ b/dump/win_dump.c
@@ -14,14 +14,74 @@
 #include "qemu/error-report.h"
 #include "exec/cpu-defs.h"
 #include "hw/core/cpu.h"
+#include "hw/misc/vmcoreinfo.h"
 #include "qemu/win_dump_defs.h"
 #include "win_dump.h"
 #include "cpu.h"
+#include "elf.h"
 
 #if defined(TARGET_X86_64)
 
+#define ELF_NOTE_SIZE(hdr_size, name_size, desc_size)   \
+    ((DIV_ROUND_UP((hdr_size), 4) +                     \
+      DIV_ROUND_UP((name_size), 4) +                    \
+      DIV_ROUND_UP((desc_size), 4)) * 4)
+
 bool win_dump_available(Error **errp)
 {
+    uint64_t addr, note_head_size, name_size, desc_size;
+    uint32_t size;
+    uint16_t guest_format;
+    uint8_t *guest_note = NULL;
+    size_t guest_note_size = 0;
+    VMCoreInfoState *vmci = vmcoreinfo_find();
+    ArchDumpInfo dump_info = {};
+    GuestPhysBlockList blocks = {};
+    int ret;
+
+    if (!vmci || !vmci->has_vmcoreinfo)
+        return false;
+
+    ret = cpu_get_dump_info(&dump_info, &blocks);
+    if (ret < 0)
+        return false;
+
+    guest_format = le16_to_cpu(vmci->vmcoreinfo.guest_format);
+    if (guest_format != FW_CFG_VMCOREINFO_FORMAT_ELF)
+        return false;
+
+    size = le32_to_cpu(vmci->vmcoreinfo.size);
+    addr = le64_to_cpu(vmci->vmcoreinfo.paddr);
+    note_head_size = dump_info.d_class == ELFCLASS64 ?
+        sizeof(Elf64_Nhdr) : sizeof(Elf32_Nhdr);
+
+    guest_note = g_malloc(size + 1);
+    cpu_physical_memory_read(addr, guest_note, size);
+    if (dump_info.d_class == ELFCLASS64) {
+        const Elf64_Nhdr *hdr = (void *)guest_note;
+        if (dump_info.d_endian == ELFDATA2LSB) {
+            name_size = cpu_to_le64(hdr->n_namesz);
+            desc_size = cpu_to_le64(hdr->n_descsz);
+        } else {
+            name_size = cpu_to_be64(hdr->n_namesz);
+            desc_size = cpu_to_be64(hdr->n_descsz);
+        }
+    } else {
+        const Elf32_Nhdr *hdr = (void *)guest_note;
+        if (dump_info.d_endian == ELFDATA2LSB) {
+            name_size = cpu_to_le32(hdr->n_namesz);
+            desc_size = cpu_to_le32(hdr->n_descsz);
+        } else {
+            name_size = cpu_to_be32(hdr->n_namesz);
+            desc_size = cpu_to_be32(hdr->n_descsz);
+        }
+    }
+
+    guest_note_size = ELF_NOTE_SIZE(note_head_size, name_size, desc_size);
+    if (guest_note_size != VMCOREINFO_WIN_DUMP_NOTE_SIZE64 &&
+        guest_note_size != VMCOREINFO_WIN_DUMP_NOTE_SIZE32)
+        return false;
+
     return true;
 }
 
-- 
2.47.3