On Mon, 2015-08-24 at 15:12 +0800, Dongsheng Yang wrote: > On 08/24/2015 03:02 PM, Artem Bityutskiy wrote: > > On Mon, 2015-08-24 at 09:29 +0800, Dongsheng Yang wrote: > > > On 08/10/2015 10:46 AM, Dongsheng Yang wrote: > > > > On 08/09/2015 05:17 AM, Richard Weinberger wrote: > > > > > Am 30.07.2015 um 07:48 schrieb Dongsheng Yang: > > > > > > We need to set or clear MS_RDONLY in remounting. > > > > > > > > > > Care to explain why? > > > > > Does the quota subsystem need that information? > > > > > If so, where? > > > > > > > > Ha, yes, you are right. > > > > > > > > When we remount to rw from ro, we need to call dquot_resume. > > > > And dquot_resume will call vfs_load_quota_inode() which > > > > will check the MS_RDONLY. If it's ro mode, will return > > > > an -EROFS. > > > > > > > > And I know that we are using ->ro_mount in ubifs > > > > to store the mounted mode. So we don't care about > > > > the MS_RDONLY in ubifs. But why not to tell vfs we are in > > > > ro or rw? Does it cause any problem? > > > > > > Hi Artem, > > > I found there is a commit 2ef13294d to introduce > > > ro_mount to ubifs. Yes, I see the reason to use ro_mount > > > rather than MS_RDONLY in ubifs. But why we do not set > > > MS_RDONLY to tell vfs it's in rdonly or not? Current > > > quota depends on it. Does this patch cause some problem? > > > > MS_RDONLY is set at mount time, then it can be changed when we re > > -mount, and then UBIFS can change it when there was a critical > > error, > > to ask VFS to stop writing more data to the file-system. See > > 'ubifs_ro_mode()'. > > > > The custom ro_mount is the same as MS_RDONLY, but it does not > > change in > > 'ubifs_ro_mode()'. It preserves the last mount state before the > > error > > happened - was it R/O or R/W. > > > > Why is this needed? > > > > UBIFS allocate different amount of resources depending on whether > > we > > are R/O or R/W. We use less memory in R/O mode, for example. > > > > At unmount time, we need to know whether we allocated the "RW" > > amount > > of resources or the "RO" amount of resources. > > > > We cannot use the MS_RDONLY flag to detect that, because it is > > changed > > in 'ubifs_ro_mode()' unconditionally, so we lose the information. > > Therefore we use the custom ro_mount flag - it tells us how we were > > mounted, so we know how much resources to free. > > Great explanation!!! This makes it much more clear to me. > > But about: > > MS_RDONLY is set at mount time, then it can be changed when we re > > Currently, ubifs did not set it at mount time and ubifs did not > change > it in re-mounting. So vfs don't know the R/O or R/W mode of ubifs. Well, sounds like a bug. Either we missed that, or VFS used to set it, and now does not. In either case, IIUC, the MS_RDONLY flag should be set on remount and reflect the mount state. Please, verify /proc/mounts after RO<->RW remounts - we must make sure mount options are correct there. You can cook a patch and send it. Do not forget to add the stable tag then. Artem. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
