From 6d41807614151829ae17a3a58bff8572af5e407e Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Mon, 10 Aug 2009 16:03:43 -0400 Subject: [PATCH 1/2] ext3: Update Kconfig description of EXT3_DEFAULTS_TO_ORDERED The old description for this configuration option was perhaps not completely balanced in terms of describing the tradeoffs of using a default of data=writeback vs. data=ordered. Despite the fact that old description very strongly recomended disabling this feature, all of the major distributions have elected to preserve the existing 'legacy' default, which is a strong hint that it perhaps wasn't telling the whole story. This revised description has been vetted by a number of ext3 developers as being better at informing the user about the tradeoffs of enabling or disabling this configuration feature. Cc: linux-ext4@vger.kernel.org Signed-off-by: "Theodore Ts'o" Signed-off-by: Jan Kara --- fs/ext3/Kconfig | 28 +++++++++++++++------------- 1 file changed, 15 insertions(+), 13 deletions(-) diff --git a/fs/ext3/Kconfig b/fs/ext3/Kconfig index fb3c1a21b135..522b15498f45 100644 --- a/fs/ext3/Kconfig +++ b/fs/ext3/Kconfig @@ -29,23 +29,25 @@ config EXT3_FS module will be called ext3. config EXT3_DEFAULTS_TO_ORDERED - bool "Default to 'data=ordered' in ext3 (legacy option)" + bool "Default to 'data=ordered' in ext3" depends on EXT3_FS help - If a filesystem does not explicitly specify a data ordering - mode, and the journal capability allowed it, ext3 used to - historically default to 'data=ordered'. + The journal mode options for ext3 have different tradeoffs + between when data is guaranteed to be on disk and + performance. The use of "data=writeback" can cause + unwritten data to appear in files after an system crash or + power failure, which can be a security issue. However, + "data=ordered" mode can also result in major performance + problems, including seconds-long delays before an fsync() + call returns. For details, see: - That was a rather unfortunate choice, because it leads to all - kinds of latency problems, and the 'data=writeback' mode is more - appropriate these days. + http://ext4.wiki.kernel.org/index.php/Ext3_data_mode_tradeoffs - You should probably always answer 'n' here, and if you really - want to use 'data=ordered' mode, set it in the filesystem itself - with 'tune2fs -o journal_data_ordered'. - - But if you really want to enable the legacy default, you can do - so by answering 'y' to this question. + If you have been historically happy with ext3's performance, + data=ordered mode will be a safe choice and you should + answer 'y' here. If you understand the reliability and data + privacy issues of data=writeback and are willing to make + that trade off, answer 'n'. config EXT3_FS_XATTR bool "Ext3 extended attributes" From 3c4cec65274481ec6332b0a91f19b4c8c5394801 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Mon, 24 Aug 2009 16:38:43 +0200 Subject: [PATCH 2/2] ext3: Improve error message that changing journaling mode on remount is not possible This patch makes the error message about changing journaling mode on remount more descriptive. Some people are going to hit this error now due to commit bbae8bcc49bc4d002221dab52c79a50a82e7cd1f if they configure a kernel to default to data=writeback mode. The problem happens if they have data=ordered set for the root filesystem in /etc/fstab but not in the kernel command line (and they don't use initrd). Their filesystem then gets mounted as data=writeback by kernel but then their boot fails because init scripts won't be able to remount the filesystem rw. Better error message will hopefully make it easier for them to find the error in their setup and bother us less with error reports :). Signed-off-by: Jan Kara --- fs/ext3/super.c | 40 +++++++++++++++++++++++++++------------- 1 file changed, 27 insertions(+), 13 deletions(-) diff --git a/fs/ext3/super.c b/fs/ext3/super.c index 524b349c6299..a8d80a7f1105 100644 --- a/fs/ext3/super.c +++ b/fs/ext3/super.c @@ -543,6 +543,19 @@ static inline void ext3_show_quota_options(struct seq_file *seq, struct super_bl #endif } +static char *data_mode_string(unsigned long mode) +{ + switch (mode) { + case EXT3_MOUNT_JOURNAL_DATA: + return "journal"; + case EXT3_MOUNT_ORDERED_DATA: + return "ordered"; + case EXT3_MOUNT_WRITEBACK_DATA: + return "writeback"; + } + return "unknown"; +} + /* * Show an option if * - it's set to a non-default value OR @@ -616,13 +629,8 @@ static int ext3_show_options(struct seq_file *seq, struct vfsmount *vfs) if (test_opt(sb, NOBH)) seq_puts(seq, ",nobh"); - if (test_opt(sb, DATA_FLAGS) == EXT3_MOUNT_JOURNAL_DATA) - seq_puts(seq, ",data=journal"); - else if (test_opt(sb, DATA_FLAGS) == EXT3_MOUNT_ORDERED_DATA) - seq_puts(seq, ",data=ordered"); - else if (test_opt(sb, DATA_FLAGS) == EXT3_MOUNT_WRITEBACK_DATA) - seq_puts(seq, ",data=writeback"); - + seq_printf(seq, ",data=%s", data_mode_string(sbi->s_mount_opt & + EXT3_MOUNT_DATA_FLAGS)); if (test_opt(sb, DATA_ERR_ABORT)) seq_puts(seq, ",data_err=abort"); @@ -1024,12 +1032,18 @@ static int parse_options (char *options, struct super_block *sb, datacheck: if (is_remount) { if ((sbi->s_mount_opt & EXT3_MOUNT_DATA_FLAGS) - != data_opt) { - printk(KERN_ERR - "EXT3-fs: cannot change data " - "mode on remount\n"); - return 0; - } + == data_opt) + break; + printk(KERN_ERR + "EXT3-fs (device %s): Cannot change " + "data mode on remount. The filesystem " + "is mounted in data=%s mode and you " + "try to remount it in data=%s mode.\n", + sb->s_id, + data_mode_string(sbi->s_mount_opt & + EXT3_MOUNT_DATA_FLAGS), + data_mode_string(data_opt)); + return 0; } else { sbi->s_mount_opt &= ~EXT3_MOUNT_DATA_FLAGS; sbi->s_mount_opt |= data_opt;