With the shutdown rework, it became very clear that we needed to make atomic state changes to the mount so that shutdown would be run once and once only. To do this, we used the mp->m_sb_lock as a serialisation mechanism rather than introduce a new single use spinlock for this purpose. However, what we really need to is to separate the operational state changes from static feature flag information kept in the mp->m_flags field. This would allow the m_flags field to remain largely read-only, and we can make the operational state use atomic bit operations to set, check and clear the current state. This separation between state and features was done for the log as part of the shutdown cleanup work. Reworking the way the xfs mount feature flags are used is a much bigger undertaking, hence this separate patchset. One of the big things we need to address is that features for the xfs mount can come from multiple sources. They can come from on-disk state via flags in the superblock, mount options, proc and sysfs variables, and so on. Each different mechanism has it's own special way of setting what is effectively read-only boolean state in the xfs mount that is then checked at runtime by executing code. In some cases, these boolean checks can be expensive because we have to do multiple cheaks and mask variables in the superblock to get the flag information. The naming can be verbose, and the combination of open coded flag checks vs wrapper based flag checks does little to improve the readability of the code. To clean all this up, introduce a m_features field and a m_opstate field. The m_features field holds all the features the filesysetm has enabled or disabled, and the m_opstate field holds all the atomic operational state. m_features is currently a 64 bit variable with on-disk features starting at bit 0 counting up and mount features starting at bit 63 and counting down. At the end of the series, we have roughly 26 on-disk and 16 mount feature flags used, so there's still plenty of flag space available for future additions. The result of moving all the feature flags to the mount is that we get rid of all the xfs_sb_version_has() wrappers in libxfs/xfs_format.h. We really want this file to contain the on-disk format defintion, not code used to access or interpret it. This gets rid of a large amount of boiler plate wrappers from this file and replaces them with mount features checks which are much simpler and lower overhead. Getting rid of all the sueprblock feature checks reduces the code size by about 5kB on x86-64. There are about 400 xfs_sb_version_has() feature checks in the code, so saving a few instructions on every check ends up making a substantial difference to code size. It also means this patchset is rather large.... There are a few cleanups needed before the patch set starts. We need to fix up the attr2/noattr2 mount option/superblock bit issues, as well as properly namespace some internal attribute code so we can use the global "xfs_" namespace for global feature and operational state functions. There are many further cleanups that can be done following on from this patch set. e.g the xfs_mount has several boolean state/flag fields that can be moved into the m_opstate and/or m_features variables, we can shadow state and or features into the log fields so the log doesn't need to access the xfs_mount to check current state, runtime quota state can move into the m_opstate field instead of needing separate flags, etc. This passes fstests for all the simple configurations (defaults, quotas, different directory block sizes, etc) without regressions, so nothing has been obviously broken. The only obvious issue is xfs/187, which expects "-o noattr2" to remove feature bits from the superblock and this behaviour is explicitly removed during this patchset. It is not clear if xfs/187 is a valid test to perform anymore now that noattr2 behaves this way. Version 3: - only need a single call to xfs_attr_lookup() - fix rebase mis-merge of attr2 mount flag setting. - set the realtime feature flag correctly when adding a rt device via growfs - fixed attr2 upgrade behaviour regressions. Version 2: - https://lore.kernel.org/linux-xfs/20210810052451.41578-1-david@xxxxxxxxxxxxx/ - rebased on 5.14-rc4 + for-next + "xfs: strictly order log start records" - added comment about not using bp->b_bn directly for the buffer disk address. - fix typos in commit messages - Fixed incorrect feature flag macro definitions in original introduction patch rather than fixing them in a subsequent patch. - Updated open coded superblock checks to check sparse inodes directly instead of via xfs_sb_has_incompat_feature(). - use xfs_has_v3inodes() consistently in inode size/version checks. Version 1: - https://lore.kernel.org/linux-xfs/20210714041912.2625692-1-david@xxxxxxxxxxxxx/ - based on 5.14-rc1 + "xfs: strictly order log start records"
