kernel/linux.git/Documentation/driver-api/early-userspace/buffer-format.rst, branch v6.18.21

docs: initramfs: file data alignment via name padding

2025-08-20T23:02:56+00:00

The existing cpio extraction logic reads (maximum PATH_MAX) name_len bytes from the archive into the collected name buffer and ensures that the trailing byte is a null-terminator. This allows the actual file name to be shorter than name_len, with the name string simply zero-terminated prior to the last byte. Initramfs generators, such as dracut-cpio[1], can take advantage of name zero-padding to align file data segments within the archive to filesystem block boundaries. Block boundary alignment may allow the copy_file_range syscall to reflink archive source and destination extents. Link: https://github.com/dracutdevs/dracut/commit/300e4b116c624bca1b9e7251708b1ae656fe9157 [1] Signed-off-by: David Disseldorp Reviewed-by: Nicolas Schier Link: https://lore.kernel.org/r/20250819032607.28727-7-ddiss@suse.de Signed-off-by: Nathan Chancellor

docs: initramfs: update compression and mtime descriptions

2025-04-07T07:38:01+00:00

Update the document to reflect that initramfs didn't replace initrd following kernel 2.5.x. The initramfs buffer format now supports many compression types in addition to gzip, so include them in the grammar section. c_mtime use is dependent on CONFIG_INITRAMFS_PRESERVE_MTIME. Signed-off-by: David Disseldorp Link: https://lore.kernel.org/r/20250402033949.852-2-ddiss@suse.de Reviewed-by: Randy Dunlap Signed-off-by: Christian Brauner

docs: early-userspace: move to driver-api guide

2019-07-15T14:03:01+00:00

Those documents describe a kAPI. So, add to the driver-api book. Signed-off-by: Mauro Carvalho Chehab