[01/19] fs: new API for handling inode->i_version

Message ID	20171213142017.23653-2-jlayton@kernel.org (mailing list archive)
State	New, archived
Headers	show Return-Path: <linux-fsdevel-owner@kernel.org> DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DD2C2218BC From: Jeff Layton <jlayton@kernel.org> To: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org, hch@lst.de, neilb@suse.de, bfields@fieldses.org, amir73il@gmail.com, jack@suse.de, viro@zeniv.linux.org.uk Subject: [PATCH 01/19] fs: new API for handling inode->i_version Date: Wed, 13 Dec 2017 09:19:59 -0500 Message-Id: <20171213142017.23653-2-jlayton@kernel.org> In-Reply-To: <20171213142017.23653-1-jlayton@kernel.org> References: <20171213142017.23653-1-jlayton@kernel.org> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk

diff --git a/include/linux/fs.h b/include/linux/fs.h index 511fbaabf624..5001e77342fd 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2036,19 +2036,203 @@ static inline void inode_dec_link_count(struct inode *inode) mark_inode_dirty(inode); } +/* + * The change attribute (i_version) is mandated by NFSv4 and is mostly for + * knfsd, but is also used for other purposes (e.g. IMA). The i_version must + * appear different to observers if there was a change to the inode's data or + * metadata since it was last queried. + * + * It should be considered an opaque value by observers. If it remains the same + * since it was last checked, then nothing has changed in the inode. If it's + * different then something has changed. Observers cannot infer anything about + * the nature or magnitude of the changes from the value, only that the inode + * has changed in some fashion. + * + * Not all filesystems properly implement the i_version counter. Subsystems that + * want to use i_version field on an inode should first check whether the + * filesystem sets the SB_I_VERSION flag (usually via the IS_I_VERSION macro). + * + * Those that set SB_I_VERSION will automatically have their i_version counter + * incremented on writes to normal files. If the SB_I_VERSION is not set, then + * the VFS will not touch it on writes, and the filesystem can use it how it + * wishes. Note that the filesystem is always responsible for updating the + * i_version on namespace changes in directories (mkdir, rmdir, unlink, etc.). + * We consider these sorts of filesystems to have a kernel-managed i_version. + * + * Note that some filesystems (e.g. NFS and AFS) just use the field to store + * a server-provided value (for the most part). For that reason, those + * filesystems do not set SB_I_VERSION. These filesystems are considered to + * have a self-managed i_version. + */ + +/** + * inode_set_iversion_raw - set i_version to the specified raw value + * @inode: inode to set + * @new: new i_version value to set + * + * Set @inode's i_version field to @new. This function is for use by + * filesystems that self-manage the i_version. + * + * For example, the NFS client stores its NFSv4 change attribute in this way, + * and the AFS client stores the data_version from the server here. + */ +static inline void +inode_set_iversion_raw(struct inode *inode, const u64 new) +{ + inode->i_version = new; +} + +/** + * inode_set_iversion - set i_version to a particular value + * @inode: inode to set + * @new: new i_version value to set + * + * Set @inode's i_version field to @new. This function is for filesystems with + * a kernel-managed i_version. + * + * For now, this just does the same thing as the _raw variant. + */ +static inline void +inode_set_iversion(struct inode *inode, const u64 new) +{ + inode_set_iversion_raw(inode, new); +} + +/** + * inode_set_iversion_queried - set i_version to a particular value and set + * flag to indicate that it has been viewed + * @inode: inode to set + * @new: new i_version value to set + * + * When loading in an i_version value from a backing store, we typically don't + * know whether it was previously viewed before being stored or not. Thus, we + * must assume that it was, to ensure that any changes will result in the + * value changing. + * + * This function will set the inode's i_version, and possibly flag the value + * as if it has already been viewed at least once. + * + * For now, this just does what inode_set_iversion does. + */ +static inline void +inode_set_iversion_queried(struct inode *inode, const u64 new) +{ + inode_set_iversion(inode, new); +} + +/** + * inode_maybe_inc_iversion - increments i_version + * @inode: inode with the i_version that should be updated + * @force: increment the counter even if it's not necessary + * + * Every time the inode is modified, the i_version field must be seen to have + * changed by any observer. + * + * In this implementation, we always increment it after taking the i_lock to + * ensure that we don't race with other incrementors. + * + * Returns true if counter was bumped, and false if it wasn't. + */ +static inline bool +inode_maybe_inc_iversion(struct inode *inode, bool force) +{ + spin_lock(&inode->i_lock); + inode->i_version++; + spin_unlock(&inode->i_lock); + return true; +} + +/** + * inode_inc_iversion - forcibly increment i_version + * @inode: inode that needs to be updated + * + * Forcbily increment the i_version field. This always results in a change to + * the observable value. + */ +static inline void +inode_inc_iversion(struct inode *inode) +{ + inode_maybe_inc_iversion(inode, true); +} + /** - * inode_inc_iversion - increments i_version - * @inode: inode that need to be updated + * inode_iversion_need_inc - is the i_version in need of being incremented? + * @inode: inode to check * - * Every time the inode is modified, the i_version field will be incremented. - * The filesystem has to be mounted with i_version flag + * Returns whether the inode->i_version counter needs incrementing on the next + * change. + * + * For now, we assume that it always does. */ +static inline bool +inode_iversion_need_inc(struct inode *inode) +{ + return true; +} -static inline void inode_inc_iversion(struct inode *inode) +/** + * inode_peek_iversion_raw - grab a "raw" iversion value + * @inode: inode from which i_version should be read + * + * Grab a "raw" inode->i_version value and return it. The i_version is not + * flagged or converted in any way. This is mostly used to access a self-managed + * i_version. + * + * With those filesystems, we want to treat the i_version as an entirely + * opaque value. + */ +static inline u64 +inode_peek_iversion_raw(const struct inode *inode) +{ + return inode->i_version; +} + +/** + * inode_peek_iversion - read i_version without flagging it to be incremented + * @inode: inode from which i_version should be read + * + * Read the inode i_version counter for an inode without registering it as a + * query. + * + * This is typically used by local filesystems that need to store an i_version + * on disk. In that situation, it's not necessary to flag it as having been + * viewed, as the result won't be used to gauge changes from that point. + */ +static inline u64 +inode_peek_iversion(const struct inode *inode) +{ + return inode_peek_iversion_raw(inode); +} + +/** + * inode_query_iversion - read i_version for later use + * @inode: inode from which i_version should be read + * + * Read the inode i_version counter. This should be used by callers that wish + * to store the returned i_version for later comparison. This will guarantee + * that a later query of the i_version will result in a different value if + * anything has changed. + * + * This implementation just does a peek. + */ +static inline u64 +inode_query_iversion(struct inode *inode) +{ + return inode_peek_iversion(inode); +} + +/** + * inode_cmp_iversion - check whether the i_version counter has changed + * @inode: inode to check + * @old: old value to check against its i_version + * + * Compare an i_version counter with a previous one. Returns 0 if they are + * the same or non-zero if they are different. + */ +static inline s64 +inode_cmp_iversion(const struct inode *inode, const u64 old) { - spin_lock(&inode->i_lock); - inode->i_version++; - spin_unlock(&inode->i_lock); + return (s64)inode_peek_iversion(inode) - (s64)old; } enum file_time_flags {

[01/19] fs: new API for handling inode->i_version

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