On Tue, Nov 02, 2021 at 04:11:06PM +0800, Michael Chang via Grub-devel wrote: > Up to now grub can only embed to the first 64 KiB before primary
s/grub/GRUB/ > superblock of btrfs, effectively limiting the size that could > consequently pose restrictions to feature enablement like advancing zstd s/advancing/advanced/? > compression. > > This patch attempts to utilize full unused area reserved by btrfs for > bootloader outlined in the document [1] where this paragraph quoted. > > "The first 1MiB on each device is unused with the exception of primary > superblock that is on the offset 64KiB and spans 4KiB." > > Apart from that, adjacent sectors to superblock and first block group > are not used for embedding in case of overflow and it's tracing. What do you mean by "it's tracing" here? > This patch has been tested to provide out of the box support to btrfs > zstd compression with which grub has been installed to the partition. s/grub/GRUB/ > [1] > https://btrfs.wiki.kernel.org/index.php/Manpage/btrfs(5)#BOOTLOADER_SUPPORT > > Signed-off-by: Michael Chang <mch...@suse.com> > --- > grub-core/fs/btrfs.c | 80 +++++++++++++++++++++++++++++++++++++------- > 1 file changed, 67 insertions(+), 13 deletions(-) > > diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c > index 63203034d..dcd4635f1 100644 > --- a/grub-core/fs/btrfs.c > +++ b/grub-core/fs/btrfs.c > @@ -2159,6 +2159,35 @@ grub_btrfs_label (grub_device_t device, char **label) > } > > #ifdef GRUB_UTIL > + > +struct embed_region { > + unsigned int offset; s/offset/start/ > + unsigned int len; s/len/secs/ > +}; > + > +#define KB_TO_SECTOR(x) ((x) << 1) I think this macro belongs to the include/grub/disk.h. Additionally, it should be named, e.g., KiB_TO_GRUB_DISK_SECS and use GRUB_DISK_SECTOR_BITS. > +/* > + * > https://btrfs.wiki.kernel.org/index.php/Manpage/btrfs(5)#BOOTLOADER_SUPPORT > + * The first 1MiB on each device is unused with the exception of primary > + * superblock that is on the offset 64KiB and spans 4KiB. > + */ > + > +static const struct { > + struct embed_region available; > + struct embed_region used[6]; > +} area = { s/area/btrfs_head/? > + .available = {0, KB_TO_SECTOR(1024)}, /* The first 1MiB */ Missing space between KB_TO_SECTOR and "(". > + .used = { > + {0, 1}, /* boot.S */ > + {KB_TO_SECTOR(64) - 1, 1}, /* overflow guard */ Ditto and below... > + {KB_TO_SECTOR(64), KB_TO_SECTOR(4)}, /* 4KiB superblock */ > + {KB_TO_SECTOR(68), 1}, /* overflow guard */ > + {KB_TO_SECTOR(1024) - 1, 1}, /* overflow guard */ > + {0, 0} /* array terminator */ > + } > +}; > + > static grub_err_t > grub_btrfs_embed (grub_device_t device __attribute__ ((unused)), > unsigned int *nsectors, > @@ -2166,25 +2195,50 @@ grub_btrfs_embed (grub_device_t device __attribute__ > ((unused)), > grub_embed_type_t embed_type, > grub_disk_addr_t **sectors) > { > - unsigned i; > + unsigned int i, j; > + const struct embed_region *u; > + grub_disk_addr_t *map; > + unsigned int n = 0; > > if (embed_type != GRUB_EMBED_PCBIOS) > return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET, > "BtrFS currently supports only PC-BIOS embedding"); > > - if (64 * 2 - 1 < *nsectors) > - return grub_error (GRUB_ERR_OUT_OF_RANGE, > - N_("your core.img is unusually large. " > - "It won't fit in the embedding area")); > - > - *nsectors = 64 * 2 - 1; > - if (*nsectors > max_nsectors) > - *nsectors = max_nsectors; > - *sectors = grub_calloc (*nsectors, sizeof (**sectors)); > - if (!*sectors) > + map = grub_calloc (area.available.len, sizeof (*map)); > + if (!map) if (map == NULL) > return grub_errno; > - for (i = 0; i < *nsectors; i++) > - (*sectors)[i] = i + 1; > + > + for (u = area.used; u->len; ++u) > + { > + unsigned int end = u->offset + u->len; > + > + if (end > area.available.len) > + end = area.available.len; > + for (i = u->offset; i < end; ++i) > + map[i] = 1; > + } > + > + for (i = 0; i < area.available.len; ++i) > + if (map[i] == 0) > + n++; > + > + if (n < *nsectors) > + { > + grub_free (map); > + return grub_error (GRUB_ERR_OUT_OF_RANGE, > + N_("your core.img is unusually large. " > + "It won't fit in the embedding area")); > + } > + > + if (n > max_nsectors) > + n = max_nsectors; > + > + for (i = 0, j = 0; i < area.available.len && j < n; ++i) > + if (map[i] == 0) > + map[j++] = area.available.offset + i; I am not fully sure what is happening in this loop. In general I would be happy if you add more comments before each step in the code above. Daniel _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
