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

[Atsushi Kumagai]

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))