Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932252Ab1FGWUD (ORCPT ); Tue, 7 Jun 2011 18:20:03 -0400 Received: from mail-gy0-f174.google.com ([209.85.160.174]:58422 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932227Ab1FGWUA (ORCPT ); Tue, 7 Jun 2011 18:20:00 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:x-mailer:in-reply-to:references; b=hPqC5qYzHVxv4/yFPhLLrcE2wRz+lFAImtsFdIXgvTECywH+vJQUUhi19LtrCnlmtY n2FvAZoAI8Wt2l/6II++rmmxdYMl2XbmxUimOCX9AaMxBNWNUctryZPqblXk77zK5iHb QUWtDhps/hdmTYlB2e88BNaFtxGxYtDLs6/a0= From: Will Drewry To: linux-kernel@vger.kernel.org Cc: Kay Sievers , Will Drewry , Jens Axboe , Andrew Morton , Namhyung Kim , Trond Myklebust Subject: [PATCH v2] init: add root=PARTUUID=UUID,PARTNROFF=%d support Date: Tue, 7 Jun 2011 17:19:33 -0500 Message-Id: <1307485173-32010-1-git-send-email-wad@chromium.org> X-Mailer: git-send-email 1.7.0.4 In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4328 Lines: 122 Expand root=PARTUUID=UUID syntax to support selecting a root partition by integer offset from a known, unique partition. This approach provides similar properties to specifying a device and partition number, but using the UUID as the unique path prior to evaluating the offset. For example, root=PARTUUID=99DE9194-FC15-4223-9192-FC243948F88B,PARTNROFF=1 selects the partition with UUID 99DE.. then select the next partition. This change is motivated by a particular usecase in Chromium OS where the bootloader can easily determine what partition it is on (by UUID) but doesn't perform general partition table walking. That said, support for this model provides a direct mechanism for the user to modify the root partition to boot without specifically needing to extract each UUID or update the bootloader explicitly when the root partition UUID is changed (if it is recreated to be larger, for instance). Pinning to a /boot-style partition UUID allows the arbitrary root partition reconfiguration/modifications with slightly less ambiguity than just [dev][partition] and less stringency than the specific root partition UUID. At present, PARTNROFF is tied to PARTUUID use and must follow immediately. It is possible to expand support to other values of root= or to add other key-value attributes and orderings, but it seems unnecessary to add the infrastructure without a concrete need. v2: - convert from +/-%u to ,PARTNROFF=%d Signed-off-by: Will Drewry --- init/do_mounts.c | 34 ++++++++++++++++++++++++++++++---- 1 files changed, 30 insertions(+), 4 deletions(-) diff --git a/init/do_mounts.c b/init/do_mounts.c index c0851a8..35329b2 100644 --- a/init/do_mounts.c +++ b/init/do_mounts.c @@ -85,12 +85,15 @@ no_match: /** * devt_from_partuuid - looks up the dev_t of a partition by its UUID - * @uuid: 36 byte char array containing a hex ascii UUID + * @uuid: min 36 byte char array containing a hex ascii UUID * * The function will return the first partition which contains a matching * UUID value in its partition_meta_info struct. This does not search * by filesystem UUIDs. * + * If @uuid is followed by a ",PARTNROFF=%d", then the number will be + * extracted and used as an offset from the partition identified by the UUID. + * * Returns the matching dev_t on success or 0 on failure. */ static dev_t devt_from_partuuid(char *uuid_str) @@ -98,6 +101,16 @@ static dev_t devt_from_partuuid(char *uuid_str) dev_t res = 0; struct device *dev = NULL; u8 uuid[16]; + struct gendisk *disk; + struct hd_struct *part; + int offset = 0; + + if (strlen(uuid_str) < 36) + goto done; + + /* Check for optional partition number offset attributes. */ + if (uuid_str[36]) + sscanf(&uuid_str[36], ",PARTNROFF=%d", &offset); /* Pack the requested UUID in the expected format. */ part_pack_uuid(uuid_str, uuid); @@ -107,8 +120,21 @@ static dev_t devt_from_partuuid(char *uuid_str) goto done; res = dev->devt; - put_device(dev); + /* Attempt to find the partition by offset. */ + if (!offset) + goto no_offset; + + res = 0; + disk = part_to_disk(dev_to_part(dev)); + part = disk_get_part(disk, dev_to_part(dev)->partno + offset); + if (part) { + res = part_devt(part); + put_device(part_to_dev(part)); + } + +no_offset: + put_device(dev); done: return res; } @@ -126,6 +152,8 @@ done: * used when disk name of partitioned disk ends on a digit. * 6) PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF representing the * unique id of a partition if the partition table provides it. + * 7) PARTUUID=,PARTNROFF= to select a partition in relation to + * a partition with a known unique id. * * If name doesn't have fall into the categories above, we return (0,0). * block_class is used to check if something is a disk name. If the disk @@ -143,8 +171,6 @@ dev_t name_to_dev_t(char *name) #ifdef CONFIG_BLOCK if (strncmp(name, "PARTUUID=", 9) == 0) { name += 9; - if (strlen(name) != 36) - goto fail; res = devt_from_partuuid(name); if (!res) goto fail; -- 1.7.0.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/