From patchwork Mon Mar 31 05:03:30 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Disseldorp X-Patchwork-Id: 14033159 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EAF8486338 for ; Mon, 31 Mar 2025 05:03:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.130 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743397430; cv=none; b=XG1+77N9ZJkK13rpeoNNBtq3ocdQ1IpZHtGpN+uZXOZv3GAjNv/Lj4jX9dxnigbFgREC2JA13IOYtmCnBpvEzt9Ib2Bmm7ecpz7fpOO2DpFDbPPmaSlpOZVFCXKmHc+ZZ0mT/Mn+bnuzj7z3LvbgiykNTQExSVsrG8HwMbJQQOI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743397430; c=relaxed/simple; bh=kM0h3uBUOPgkpJ5JBHLk/JkyxoqZM3lgR27h3GeCfzw=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=gWPWmilHhfPwoBUuLKbF8u0+Wjovod12Ix9gML55WvDXEHGAO6JvFr9EIKXdyWQojLqV3mbf065qLBx3BdFEjRFkxGgyfTJsoBrdYZq/f3yJbPc/4iOJmBH9UUMwbzUy7arvi88OUOzT4tB3ncpj5fgoCsLu9vR1qHLiMbOqYm4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=suse.de; spf=pass smtp.mailfrom=suse.de; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b=U5P6y/Ob; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b=ol79eBre; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b=U5P6y/Ob; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b=ol79eBre; arc=none smtp.client-ip=195.135.223.130 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="U5P6y/Ob"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="ol79eBre"; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="U5P6y/Ob"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="ol79eBre" Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 0439A21186; Mon, 31 Mar 2025 05:03:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1743397427; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=HmWKMkt9Y89ko/jG/wBS1+lg6w+9nyUnY4rWTTkWcsg=; b=U5P6y/OblGif2sfeKs7gdURDx2QiSqsHpDVUm0tAfTsX63gQpJndR9AbbM3rV/zsS7grwu 07s2M5y6iRDlkUBx9OMNpMfjJTBPf/633WFKy5PftuZVJUDjTvj0fV18/SyUa9BpnEEe4e gsCoNNtnz687nt/J/ycI+kaNgOg74nw= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1743397427; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=HmWKMkt9Y89ko/jG/wBS1+lg6w+9nyUnY4rWTTkWcsg=; b=ol79eBrezz0BNfdcCiv7uwMMnj9X5Pm1AMfd0wp9mf+oCu5BM2DY+KJIJ4SC9ss9y2nfSn W7TwvfWwTB/xMjBA== Authentication-Results: smtp-out1.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1743397427; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=HmWKMkt9Y89ko/jG/wBS1+lg6w+9nyUnY4rWTTkWcsg=; b=U5P6y/OblGif2sfeKs7gdURDx2QiSqsHpDVUm0tAfTsX63gQpJndR9AbbM3rV/zsS7grwu 07s2M5y6iRDlkUBx9OMNpMfjJTBPf/633WFKy5PftuZVJUDjTvj0fV18/SyUa9BpnEEe4e gsCoNNtnz687nt/J/ycI+kaNgOg74nw= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1743397427; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=HmWKMkt9Y89ko/jG/wBS1+lg6w+9nyUnY4rWTTkWcsg=; b=ol79eBrezz0BNfdcCiv7uwMMnj9X5Pm1AMfd0wp9mf+oCu5BM2DY+KJIJ4SC9ss9y2nfSn W7TwvfWwTB/xMjBA== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 02AE813927; Mon, 31 Mar 2025 05:03:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 8TlxKzAi6meTfQAAD6G6ig (envelope-from ); Mon, 31 Mar 2025 05:03:44 +0000 From: David Disseldorp To: Alexander Viro , Christian Brauner Cc: linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, David Disseldorp Subject: [PATCH] docs: initramfs: update compression and mtime descriptions Date: Mon, 31 Mar 2025 16:03:30 +1100 Message-ID: <20250331050330.17161-1-ddiss@suse.de> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Spam-Level: X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_FIVE(0.00)[5]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:mid,imap1.dmz-prg2.suse.org:helo]; RCVD_TLS_ALL(0.00)[] X-Spam-Score: -2.80 X-Spam-Flag: NO 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 --- .../early-userspace/buffer-format.rst | 30 ++++++++++++------- 1 file changed, 19 insertions(+), 11 deletions(-) diff --git a/Documentation/driver-api/early-userspace/buffer-format.rst b/Documentation/driver-api/early-userspace/buffer-format.rst index 7f74e301fdf35..cb31d617729c5 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 contents is passed +using the same memory buffer protocol used by initrd, but the contents 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. 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.