Re: [PATCH / RFC] makedumpfile header to show LZO/snappy/zlib

Atsushi Kumagai
2013-09-20T04:26:16Z

Hello Dave,

(2013/09/16 0:56), Dave Anderson wrote:
>
> With the advent of LZO and snappy compression support, it would be
> helpful if it could be readily determined which type of compression
> was used to create the dumpfile.
>
> The zlib/LZO/snappy indicator is only found down in the bowels of each
> page_desc structure:
>
> /* page flags */
> #define DUMP_DH_COMPRESSED_ZLIB 0x1 /* page is compressed with zlib */
> #define DUMP_DH_COMPRESSED_LZO 0x2 /* paged is compressed with lzo */
> #define DUMP_DH_COMPRESSED_SNAPPY 0x4
> /* paged is compressed with snappy */
>
> /* descriptor of each page for vmcore */
> typedef struct page_desc {
> off_t offset; /* the offset of the page data*/
> unsigned int size; /* the size of this dump page */
> unsigned int flags; /* flags */
> unsigned long long page_flags; /* page flags */
> } page_desc_t;
>
> The compressed kdump's header does contain a "status" flag:
>
> struct disk_dump_header {
> char signature[SIG_LEN]; /* = "KDUMP " */
> int header_version; /* Dump header version */
> struct new_utsname utsname; /* copy of system_utsname */
> struct timeval timestamp; /* Time stamp */
> unsigned int status; /* Above flags */
> ...
>
> which has these 3 flags:
>
> #define DUMP_HEADER_COMPLETED 0
> #define DUMP_HEADER_INCOMPLETED 1
> #define DUMP_HEADER_COMPRESSED 8
>
> But they are all remnants of the old "diskdump" facility, and none of them
> are ever used by makedumpfile.
>
> Any chance that the LZO/snappy/zlib method could also be put up in
> the disk_dump_header?
>
> Dave
>
> --- makedumpfile-1.5.4/makedumpfile.c.orig
> +++ makedumpfile-1.5.4/makedumpfile.c
> @@ -5162,6 +5162,16 @@ write_kdump_header(void)
> dh->bitmap_blocks = divideup(info->len_bitmap, dh->block_size);
> memcpy(&dh->timestamp, &info->timestamp, sizeof(dh->timestamp));
> memcpy(&dh->utsname, &info->system_utsname, sizeof(dh->utsname));
> + if (info->flag_compress & DUMP_DH_COMPRESSED_ZLIB)
> + dh->status |= DUMP_DH_COMPRESSED_ZLIB;
> +#ifdef USELZO
> + else if (info->flag_compress & DUMP_DH_COMPRESSED_LZO)
> + dh->status |= DUMP_DH_COMPRESSED_LZO)
> +#endif
> +#ifdef USESNAPPY
> + else if (info->flag_compress & DUMP_DH_COMPRESSED_SNAPPY)
> + dh->status |= DUMP_DH_COMPRESSED_SNAPPY)
> +#endif

dh->status will not guarantee that *all pages* are compressed
by the check below:

> #ifdef USELZO
> } else if (info->flag_lzo_support
> && (info->flag_compress & DUMP_DH_COMPRESSED_LZO)
> && ((size_out = info->page_size),
> lzo1x_1_compress(buf, info->page_size, buf_out,
> &size_out, wrkmem) == LZO_E_OK)
> && (size_out < info->page_size)) {
^^^^^^^^^^^^^^^^^^^^^^^^^^^
When there is no effect of compression, the page will not be compressed.

> pd.flags = DUMP_DH_COMPRESSED_LZO;
> pd.size = size_out;
> memcpy(buf, buf_out, pd.size);
> #endif

If we are on the same page, I'll accept your patch.

Thanks
Atsushi Kumagai

>
> size = sizeof(struct disk_dump_header);
> if (!write_buffer(info->fd_dumpfile, 0, dh, size, info->name_dumpfile))