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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 Reviewed-by: Randy Dunlap --- Changes since v1 following feedback from Randy Dunlap: - contents -> content - format of the initramfs buffer format -> the initramfs buffer format .../early-userspace/buffer-format.rst | 34 ++++++++++++------- 1 file changed, 21 insertions(+), 13 deletions(-) diff --git a/Documentation/driver-api/early-userspace/buffer-format.rst b/Documentation/driver-api/early-userspace/buffer-format.rst index 7f74e301fdf35..726bfa2fe70da 100644 --- a/Documentation/driver-api/early-userspace/buffer-format.rst +++ b/Documentation/driver-api/early-userspace/buffer-format.rst @@ -4,20 +4,18 @@ initramfs buffer format Al Viro, H. Peter Anvin -Last revision: 2002-01-13 - -Starting with kernel 2.5.x, the old "initial ramdisk" protocol is -getting {replaced/complemented} with the new "initial ramfs" -(initramfs) protocol. The initramfs contents is passed using the same -memory buffer protocol used by the initrd protocol, but the contents +With kernel 2.5.x, the old "initial ramdisk" protocol was complemented +with an "initial ramfs" protocol. The initramfs content is passed +using the same memory buffer protocol used by initrd, but the content is different. The initramfs buffer contains an archive which is -expanded into a ramfs filesystem; this document details the format of -the initramfs buffer format. +expanded into a ramfs filesystem; this document details the initramfs +buffer format. The initramfs buffer format is based around the "newc" or "crc" CPIO formats, and can be created with the cpio(1) utility. The cpio -archive can be compressed using gzip(1). One valid version of an -initramfs buffer is thus a single .cpio.gz file. +archive can be compressed using gzip(1), or any other algorithm provided +via CONFIG_DECOMPRESS_*. One valid version of an initramfs buffer is +thus a single .cpio.gz file. The full format of the initramfs buffer is defined by the following grammar, where:: @@ -25,12 +23,20 @@ grammar, where:: * is used to indicate "0 or more occurrences of" (|) indicates alternatives + indicates concatenation - GZIP() indicates the gzip(1) of the operand + GZIP() indicates gzip compression of the operand + BZIP2() indicates bzip2 compression of the operand + LZMA() indicates lzma compression of the operand + XZ() indicates xz compression of the operand + LZO() indicates lzo compression of the operand + LZ4() indicates lz4 compression of the operand + ZSTD() indicates zstd compression of the operand ALGN(n) means padding with null bytes to an n-byte boundary - initramfs := ("\0" | cpio_archive | cpio_gzip_archive)* + initramfs := ("\0" | cpio_archive | cpio_compressed_archive)* - cpio_gzip_archive := GZIP(cpio_archive) + cpio_compressed_archive := (GZIP(cpio_archive) | BZIP2(cpio_archive) + | LZMA(cpio_archive) | XZ(cpio_archive) | LZO(cpio_archive) + | LZ4(cpio_archive) | ZSTD(cpio_archive)) cpio_archive := cpio_file* + ( | cpio_trailer) @@ -75,6 +81,8 @@ c_chksum 8 bytes Checksum of data field if c_magic is 070702; The c_mode field matches the contents of st_mode returned by stat(2) on Linux, and encodes the file type and file permissions. +c_mtime is ignored unless CONFIG_INITRAMFS_PRESERVE_MTIME=y is set. + The c_filesize should be zero for any file which is not a regular file or symlink.