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

[Dave Anderson]

----- Original Message -----
> 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.

Right, I understand.

Thanks,
  Dave


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