Re: [PATCH] btrfs: disable zstd support for i386-pc

[Daniel Kiper]

On Wed, Nov 06, 2019 at 11:15:04AM -0800, Vladimir 'phcoder' Serbinenko wrote:
> Please don't do it this way. The right solution is to move it to separate
> module and include zstd module when needed. Not everybody uses btrfs
> embedded area. I recommend not to use it. Using mbr gap or BBP is the
> recommended way.

I will put the cat among the pigeons. Maybe we should finally stop
pretending that the GRUB supports small MBR gaps. Otherwise we will
be fighting with such issues endlessly.

Daniel

> On Tue, 5 Nov 2019, 01:25 Michael Chang, <address@hidden> wrote:
>
> > The zstd support in btrfs has dependenciy to zstd module and core.img
> > grows its size significantly to 75KB on my system. The resulted image
> > cannot be installed into btrfs bootloader area in the size of 64KB and
> > eventually fails with following message.
> >
> > /usr/sbin/grub-install: warning: your core.img is unusually large.  It
> > won't fit in the embedding area.
> > /usr/sbin/grub-install: error: filesystem `btrfs' doesn't support
> > blocklists.
> >
> > The patch disabled the zstd support of btrfs in pc-bios platform to
> > avoid the regression. The resulting size is 56KB, albeit a bit too close
> > to the 64KB but works. This is simple workaround until a proper fix
> > landed upstream.
> >
> > Signed-off-by: Michael Chang <address@hidden>
> > ---
> >  grub-core/fs/btrfs.c | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> >
> > diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> > index 48bd3d04a..8f98892d3 100644
> > --- a/grub-core/fs/btrfs.c
> > +++ b/grub-core/fs/btrfs.c
> > @@ -17,6 +17,7 @@
> >   *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
> >   */
> >
> > +#ifndef GRUB_MACHINE_PCBIOS
> >  /*
> >   * Tell zstd to expose functions that aren't part of the stable API, which
> >   * aren't safe to use when linking against a dynamic library. We vendor
> > in a
> > @@ -24,6 +25,7 @@
> >   * functions to provide our own allocator, which uses grub_malloc(), to
> > zstd.
> >   */
> >  #define ZSTD_STATIC_LINKING_ONLY
> > +#endif
> >
> >  #include <grub/err.h>
> >  #include <grub/file.h>
> > @@ -35,7 +37,9 @@
> >  #include <grub/lib/crc.h>
> >  #include <grub/deflate.h>
> >  #include <minilzo.h>
> > +#ifndef GRUB_MACHINE_PCBIOS
> >  #include <zstd.h>
> > +#endif
> >  #include <grub/i18n.h>
> >  #include <grub/btrfs.h>
> >  #include <grub/crypto.h>
> > @@ -56,8 +60,10 @@ GRUB_MOD_LICENSE ("GPLv3+");
> >  #define GRUB_BTRFS_LZO_BLOCK_MAX_CSIZE (GRUB_BTRFS_LZO_BLOCK_SIZE + \
> >                                      (GRUB_BTRFS_LZO_BLOCK_SIZE / 16) + 64
> > + 3)
> >
> > +#ifndef GRUB_MACHINE_PCBIOS
> >  #define ZSTD_BTRFS_MAX_WINDOWLOG 17
> >  #define ZSTD_BTRFS_MAX_INPUT     (1 << ZSTD_BTRFS_MAX_WINDOWLOG)
> > +#endif
> >
> >  typedef grub_uint8_t grub_btrfs_checksum_t[0x20];
> >  typedef grub_uint16_t grub_btrfs_uuid_t[8];
> > @@ -229,7 +235,9 @@ struct grub_btrfs_extent_data
> >  #define GRUB_BTRFS_COMPRESSION_NONE 0
> >  #define GRUB_BTRFS_COMPRESSION_ZLIB 1
> >  #define GRUB_BTRFS_COMPRESSION_LZO  2
> > +#ifndef GRUB_MACHINE_PCBIOS
> >  #define GRUB_BTRFS_COMPRESSION_ZSTD 3
> > +#endif
> >
> >  #define GRUB_BTRFS_OBJECT_ID_CHUNK 0x100
> >
> > @@ -1229,6 +1237,7 @@ grub_btrfs_read_inode (struct grub_btrfs_data *data,
> >    return grub_btrfs_read_logical (data, elemaddr, inode, sizeof (*inode),
> > 0);
> >  }
> >
> > +#ifndef GRUB_MACHINE_PCBIOS
> >  static void *grub_zstd_malloc (void *state __attribute__((unused)),
> > size_t size)
> >  {
> >    return grub_malloc (size);
> > @@ -1318,6 +1327,7 @@ err:
> >
> >    return ret;
> >  }
> > +#endif
> >
> >  static grub_ssize_t
> >  grub_btrfs_lzo_decompress(char *ibuf, grub_size_t isize, grub_off_t off,
> > @@ -1494,8 +1504,12 @@ grub_btrfs_extent_read (struct grub_btrfs_data
> > *data,
> >
> >        if (data->extent->compression != GRUB_BTRFS_COMPRESSION_NONE
> >           && data->extent->compression != GRUB_BTRFS_COMPRESSION_ZLIB
> > +#ifndef GRUB_MACHINE_PCBIOS
> >           && data->extent->compression != GRUB_BTRFS_COMPRESSION_LZO
> >           && data->extent->compression != GRUB_BTRFS_COMPRESSION_ZSTD)
> > +#else
> > +         && data->extent->compression != GRUB_BTRFS_COMPRESSION_LZO)
> > +#endif
> >         {
> >           grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
> >                       "compression type 0x%x not supported",
> > @@ -1535,6 +1549,7 @@ grub_btrfs_extent_read (struct grub_btrfs_data *data,
> >                   != (grub_ssize_t) csize)
> >                 return -1;
> >             }
> > +#ifndef GRUB_MACHINE_PCBIOS
> >           else if (data->extent->compression ==
> > GRUB_BTRFS_COMPRESSION_ZSTD)
> >             {
> >               if (grub_btrfs_zstd_decompress (data->extent->inl,
> > data->extsize -
> > @@ -1544,6 +1559,7 @@ grub_btrfs_extent_read (struct grub_btrfs_data *data,
> >                   != (grub_ssize_t) csize)
> >                 return -1;
> >             }
> > +#endif
> >           else
> >             grub_memcpy (buf, data->extent->inl + extoff, csize);
> >           break;
> > @@ -1581,10 +1597,12 @@ grub_btrfs_extent_read (struct grub_btrfs_data
> > *data,
> >                 ret = grub_btrfs_lzo_decompress (tmp, zsize, extoff
> >                                     + grub_le_to_cpu64
> > (data->extent->offset),
> >                                     buf, csize);
> > +#ifndef GRUB_MACHINE_PCBIOS
> >               else if (data->extent->compression ==
> > GRUB_BTRFS_COMPRESSION_ZSTD)
> >                 ret = grub_btrfs_zstd_decompress (tmp, zsize, extoff
> >                                     + grub_le_to_cpu64
> > (data->extent->offset),
> >                                     buf, csize);
> > +#endif
> >               else
> >                 ret = -1;
> >
> > --
> > 2.16.4