grub-mkimage ignores compression option

[Eugene Bright]

Option --compression doesn't affect the core image size.
Does it work at all?

Running it without compression `none`
> # grub-mkimage -v -O i386-pc -p /boot btrfs -C none | wc -c
> grub-mkimage: info: the total module size is 0x1a380.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/kernel.img.
> grub-mkimage: info: locating the section .text at 0x0.
> grub-mkimage: info: locating the section .rodata at 0x5d14.
> grub-mkimage: info: locating the section .data at 0x6f40.
> grub-mkimage: info: locating the section .module_license at 0x77c0.
> grub-mkimage: info: locating the section .bss at 0x77e0.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/crypto.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/gcry_crc.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/gzio.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/diskfilter.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/raid6rec.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/lzopio.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/zstd.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/btrfs.mod.
> grub-mkimage: info: kernel_img=0x7f5fb6bc1010, kernel_size=0x77cf.
> grub-mkimage: info: the core size is 0x10092.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/lzma_decompress.img.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/diskboot.img.
> grub-mkimage: info: writing 0x200 bytes.
> grub-mkimage: info: writing 0x10ba2 bytes.
> grub-mkimage: error: cannot sync `stdout': Invalid argument.
> 69026

Running it without compression `xz`
> # grub-mkimage -v -O i386-pc -p /boot btrfs -C xz | wc -c
> grub-mkimage: info: the total module size is 0x1a380.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/kernel.img.
> grub-mkimage: info: locating the section .text at 0x0.
> grub-mkimage: info: locating the section .rodata at 0x5d14.
> grub-mkimage: info: locating the section .data at 0x6f40.
> grub-mkimage: info: locating the section .module_license at 0x77c0.
> grub-mkimage: info: locating the section .bss at 0x77e0.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/crypto.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/gcry_crc.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/gzio.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/diskfilter.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/raid6rec.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/lzopio.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/zstd.mod.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/btrfs.mod.
> grub-mkimage: info: kernel_img=0x7f42a5b1d010, kernel_size=0x77cf.
> grub-mkimage: info: the core size is 0x10092.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/lzma_decompress.img.
> grub-mkimage: info: reading /usr/lib/grub/i386-pc/diskboot.img.
> grub-mkimage: info: writing 0x200 bytes.
> grub-mkimage: info: writing 0x10ba2 bytes.
> grub-mkimage: error: cannot sync `stdout': Invalid argument.
> 69026

Is it a problem or am I missing something?

Compression could alleviate `core.img is unusually large.  It
won't fit in the embedding area.` issue.

https://lists.gnu.org/archive/html/grub-devel/2019-11/msg00057.html

--
Eugene Bright
Tel.: +380635426132