>Number: 186854 >Category: kern >Synopsis: mount a ext4 file system with uninit_bg and flex_bg in >read-only mode >Confidential: no >Severity: non-critical >Priority: low >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: update >Submitter-Id: current-users >Arrival-Date: Tue Feb 18 03:40:00 UTC 2014 >Closed-Date: >Last-Modified: >Originator: Zheng Liu >Release: current >Organization: >Environment: FreeBSD lambda 11.0-CURRENT FreeBSD 11.0-CURRENT #2 ab3f62f(master): Fri Feb 14 09:03:24 CST 2014 root@lambda:/usr/obj/home/wenqing/projects/freebsd/sys/GENERIC amd64 >Description: Currently ext2fs driver has ability to access a ext4 file system in read-only mode under some specific features. But it couldn't mount a ext4 file system that is created from scratch because uninit_bg and flex_bg features will be enabled by default. Hence the user would be trouble with this if he/she wants to access a ext4 file system with default features in read-only mode.
This patch tries to fix this issue. In the patch, all we need to do is to define a new flag set called 'EXT4F_RO_INCOMPAT_SUPP' in order to prevent the user from trying to mount a ext4 file system in read-write mode and do some sanity check. uninit_bg is a read-only compatible feature in ext4. It is used to mark which block group is uninitialised. This feature can save the time when a user creates a ext4 file system because 'mkfs' doesn't try to zero out inode/block bitmap and inode table. Meanwhile 'fsck' will skip uninitialised block group for the same purpose. flex_bg is an incompatible feature in ext4. It tries to put multiple block groups tie together as one logical block group [1]. After enabling this feature we will get more continuous disk space. 1. https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout#Flexible_Block_Groups >How-To-Repeat: mkfs.ext4 ${DEV} mount -t ext2fs -ro ${DEV} ${MNT} The user will get an error message when he/she tries to mount a ext4 file system due to some unsupported features. >Fix: The attached patch tries to fix this problem. Patch attached with submission follows: >From 94c91af45638cbaba0991f9baacf1483c5be18c4 Mon Sep 17 00:00:00 2001 From: Zheng Liu <gnehz...@gmail.com> Date: Tue, 18 Feb 2014 03:08:34 +0800 Subject: [PATCH] patch ext4fs-uninitbg-flexbg --- sys/fs/ext2fs/ext2_vfsops.c | 14 +++++++++++--- sys/fs/ext2fs/ext2fs.h | 19 ++++++++++++------- 2 files changed, 23 insertions(+), 10 deletions(-) diff --git a/sys/fs/ext2fs/ext2_vfsops.c b/sys/fs/ext2fs/ext2_vfsops.c index a18d5cc1..5c36be9 100644 --- a/sys/fs/ext2fs/ext2_vfsops.c +++ b/sys/fs/ext2fs/ext2_vfsops.c @@ -290,9 +290,10 @@ ext2_check_sb_compat(struct ext2fs *es, struct cdev *dev, int ronly) return (1); } if (es->e2fs_rev > E2FS_REV0) { - if (es->e2fs_features_incompat & ~EXT2F_INCOMPAT_SUPP) { - printf( -"WARNING: mount of %s denied due to unsupported optional features\n", + if (!ronly && + (es->e2fs_features_incompat & EXT4F_RO_INCOMPAT_SUPP)) { + printf("WARNING: R/W mount of %s denied due to " + "ext4fs only can be mounted with R/O\n", devtoname(dev)); return (1); } @@ -302,6 +303,13 @@ ext2_check_sb_compat(struct ext2fs *es, struct cdev *dev, int ronly) "unsupported optional features\n", devtoname(dev)); return (1); } + if (es->e2fs_features_incompat & + ~(EXT2F_INCOMPAT_SUPP | EXT4F_RO_INCOMPAT_SUPP)) { + printf("WARNING: mount of %s denied due to " + "unsupported optional features\n", + devtoname(dev)); + return (1); + } } return (0); } diff --git a/sys/fs/ext2fs/ext2fs.h b/sys/fs/ext2fs/ext2fs.h index b562287..05ab23d 100644 --- a/sys/fs/ext2fs/ext2fs.h +++ b/sys/fs/ext2fs/ext2fs.h @@ -201,18 +201,23 @@ struct csum { * - EXT2F_ROCOMPAT_SPARSESUPER * - EXT2F_ROCOMPAT_LARGEFILE * - EXT2F_INCOMPAT_FTYPE - * - * We partially (read-only) support the following EXT4 features: - * - EXT2F_ROCOMPAT_HUGE_FILE - * - EXT2F_ROCOMPAT_EXTRA_ISIZE - * - EXT2F_INCOMPAT_EXTENTS */ #define EXT2F_COMPAT_SUPP 0x0000 #define EXT2F_ROCOMPAT_SUPP (EXT2F_ROCOMPAT_SPARSESUPER | \ EXT2F_ROCOMPAT_LARGEFILE | \ EXT2F_ROCOMPAT_EXTRA_ISIZE) -#define EXT2F_INCOMPAT_SUPP (EXT2F_INCOMPAT_FTYPE | \ - EXT2F_INCOMPAT_EXTENTS) +#define EXT2F_INCOMPAT_SUPP (EXT2F_INCOMPAT_FTYPE) + +/* + * We partially (read-only) support the following EXT4 features: + * - EXT2F_ROCOMPAT_HUGE_FILE + * - EXT2F_ROCOMPAT_GDT_CSUM + * - EXT2F_ROCOMPAT_EXTRA_ISIZE + * - EXT2F_INCOMPAT_EXTENTS + * - EXT2F_INCOMPAT_FLEX_BG + */ +#define EXT4F_RO_INCOMPAT_SUPP (EXT2F_INCOMPAT_EXTENTS | \ + EXT2F_INCOMPAT_FLEX_BG) /* Assume that user mode programs are passing in an ext2fs superblock, not * a kernel struct super_block. This will allow us to call the feature-test -- 1.8.4.2 >Release-Note: >Audit-Trail: >Unformatted: _______________________________________________ freebsd-bugs@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-bugs To unsubscribe, send any mail to "freebsd-bugs-unsubscr...@freebsd.org"
