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Re: [Qemu-devel] [PATCH 9/9 v2] Make monitor command 'dump-guest-memory'

From: Qiao Nuohan
Subject: Re: [Qemu-devel] [PATCH 9/9 v2] Make monitor command 'dump-guest-memory' dump in kdump-compressed format
Date: Wed, 15 May 2013 13:27:20 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.5) Gecko/20120607 Thunderbird/10.0.5

On 05/15/2013 10:55 AM, Eric Blake wrote:
On 05/14/2013 08:29 PM, Qiao Nuohan wrote:
Make monitor command 'dump-guest-memory' dump in kdump-compressed format.
The command's usage:
   dump [-p] protocol [begin] [length] [format]
'format' is used to specified the format of vmcore and can be:
1. 'elf': ELF format, without compression
2. 'zlib': kdump-compressed format, with zlib-compressed
3. 'lzo': kdump-compressed format, with lzo-compressed
4. 'snappy': kdump-compressed format, with snappy-compressed
And without 'format' being set, vmcore will be in ELF format.

   1. The kdump-compressed format is readable only with the crash utility, and 
      can be smaller than the ELF format because of the compression support.
   2. The kdump-compressed format is the 5th edition.

Signed-off-by: Qiao Nuohan<address@hidden>
Signed-off-by: Zhang Xiaohe<address@hidden>

-static int dump_init(DumpState *s, int fd, bool paging, bool has_filter,
-                     int64_t begin, int64_t length, Error **errp)
+static int dump_init(DumpState *s, int fd, bool compress_format,
+                    DumpGuestMemoryFormat format, bool paging,
+                    bool has_filter, int64_t begin, int64_t length, Error 

Why do you need compress_format as a separate parameter, when that
information is redundant with the contents of format?

I need this variable to decide whether in kdump-compressed format or
not. Without using it, I need to repeat "has_format && format !=

+void qmp_dump_guest_memory(bool paging, const char *protocol, bool has_begin,
+                            int64_t begin, bool has_length,
+                            int64_t length, bool has_format,
+                            DumpGuestMemoryFormat format, Error **errp)
      const char *p;
      int fd = -1;
      DumpState *s;
      int ret;
+    int compress_format = 0;

You are using this as a bool, so type it as a bool rather than int.

Got it.

+++ b/include/sysemu/dump.h
@@ -37,6 +37,13 @@

+ * dump format
+ */
+#define FLAG_DUMP_COMPRESS_ZLIB     (0x1)   /* compressed with zlib */
+#define FLAG_DUMP_COMPRESS_LZO      (0x2)   /* compressed with lzo */
+#define FLAG_DUMP_COMPRESS_SNAPPY   (0x4)   /* compressed with snappy */

Why are you skipping 3?  Besides, these aren't flags that can be
bitwise-or'd together, so the name FLAG_ is misleading.  Why not just
make it an enum, with value 0, 1, 2 (or with 1, 2, 3)?  In fact, why
even declare this at all, instead of reusing the DumpGuestMemoryFormat
enum created for you by the QMP code generation from the schema?

Sorry about this, I didn't use these but forgot to remove them.

   * flag used in page desc of kdump-compressed format
  #define DUMP_DH_COMPRESSED_ZLIB     (0x1)
@@ -46,6 +53,7 @@
  #define KDUMP_SIGNATURE             "KDUMP   "
  #define SIG_LEN                     (sizeof(KDUMP_SIGNATURE) - 1)
  #define DISKDUMP_HEADER_BLOCKS      (1)
+#define PAGE_SIZE                   (4096)

Is that true for all platforms?

No. In "note" of patch 0/9,

"The guest should be x86 or x86_64. The other arch is not supported

PAGE_SIZE here is only supposed to support x86 or x86_64.

Qiao Nuohan

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