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

Dave Anderson
2013-09-20T13:05:05Z

----- 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))