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diff --git a/include/linux/iversion.h b/include/linux/iversion.h
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+++ b/include/linux/iversion.h
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+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_IVERSION_H
+#define _LINUX_IVERSION_H
+
+#include <linux/fs.h>
+
+/*
+ * The inode->i_version field:
+ * ---------------------------
+ * 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.
+ *
+ * Observers see the i_version as a 64-bit number that never decreases. 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.
+ *
+ * It may be impractical for filesystems to keep i_version updates atomic with
+ * respect to the changes that cause them.  They should, however, guarantee
+ * that i_version updates are never visible before the changes that caused
+ * them.  Also, i_version updates should never be delayed longer than it takes
+ * the original change to reach disk.
+ *
+ * This implementation uses the low bit in the i_version field as a flag to
+ * track when the value has been queried. If it has not been queried since it
+ * was last incremented, we can skip the increment in most cases.
+ *
+ * In the event that we're updating the ctime, we will usually go ahead and
+ * bump the i_version anyway. Since that has to go to stable storage in some
+ * fashion, we might as well increment it as well.
+ *
+ * With this implementation, the value should always appear to observers to
+ * increase over time if the file has changed. It's recommended to use
+ * inode_eq_iversion() helper to compare values.
+ *
+ * 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.
+ *
+ * Persistently storing the i_version
+ * ----------------------------------
+ * Queries of the i_version field are not gated on them hitting the backing
+ * store. It's always possible that the host could crash after allowing
+ * a query of the value but before it has made it to disk.
+ *
+ * To mitigate this problem, filesystems should always use
+ * inode_set_iversion_queried when loading an existing inode from disk. This
+ * ensures that the next attempted inode increment will result in the value
+ * changing.
+ *
+ * Storing the value to disk therefore does not count as a query, so those
+ * filesystems should use inode_peek_iversion to grab the value to be stored.
+ * There is no need to flag the value as having been queried in that case.
+ */
+
+/*
+ * We borrow the lowest bit in the i_version to use as a flag to tell whether
+ * it has been queried since we last incremented it. If it has, then we must
+ * increment it on the next change. After that, we can clear the flag and
+ * avoid incrementing it again until it has again been queried.
+ */
+#define I_VERSION_QUERIED_SHIFT (1)
+#define I_VERSION_QUERIED       (1ULL << (I_VERSION_QUERIED_SHIFT - 1))
+#define I_VERSION_INCREMENT     (1ULL << I_VERSION_QUERIED_SHIFT)
+
+/**
+ * inode_set_iversion_raw - set i_version to the specified raw value
+ * @inode: inode to set
+ * @val: new i_version value to set
+ *
+ * Set @inode's i_version field to @val. 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, u64 val)
+{
+        atomic64_set(&inode->i_version, val);
+}
+
+/**
+ * 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 atomic64_read(&inode->i_version);
+}
+
+/**
+ * inode_set_iversion - set i_version to a particular value
+ * @inode: inode to set
+ * @val: new i_version value to set
+ *
+ * Set @inode's i_version field to @val. This function is for filesystems with
+ * a kernel-managed i_version, for initializing a newly-created inode from
+ * scratch.
+ *
+ * In this case, we do not set the QUERIED flag since we know that this value
+ * has never been queried.
+ */
+static inline void
+inode_set_iversion(struct inode *inode, u64 val)
+{
+        inode_set_iversion_raw(inode, val << I_VERSION_QUERIED_SHIFT);
+}
+
+/**
+ * inode_set_iversion_queried - set i_version to a particular value as quereied
+ * @inode: inode to set
+ * @val: new i_version value to set
+ *
+ * Set @inode's i_version field to @val, and flag it for increment on the next
+ * change.
+ *
+ * Filesystems that persistently store the i_version on disk should use this
+ * when loading an existing inode from disk.
+ *
+ * When loading in an i_version value from a backing store, we can't be certain
+ * that it wasn't previously viewed before being stored. Thus, we must assume
+ * that it was, to ensure that we don't end up handing out the same value for
+ * different versions of the same inode.
+ */
+static inline void
+inode_set_iversion_queried(struct inode *inode, u64 val)
+{
+        inode_set_iversion_raw(inode, (val << I_VERSION_QUERIED_SHIFT) |
+                                I_VERSION_QUERIED);
+}
+
+/**
+ * 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.
+ *
+ * If "force" is set or the QUERIED flag is set, then ensure that we increment
+ * the value, and clear the queried flag.
+ *
+ * In the common case where neither is set, then we can return "false" without
+ * updating i_version.
+ *
+ * If this function returns false, and no other metadata has changed, then we
+ * can avoid logging the metadata.
+ */
+static inline bool
+inode_maybe_inc_iversion(struct inode *inode, bool force)
+{
+        u64 cur, old, new;
+
+        /*
+         * The i_version field is not strictly ordered with any other inode
+         * information, but the legacy inode_inc_iversion code used a spinlock
+         * to serialize increments.
+         *
+         * Here, we add full memory barriers to ensure that any de-facto
+         * ordering with other info is preserved.
+         *
+         * This barrier pairs with the barrier in inode_query_iversion()
+         */
+        smp_mb();
+        cur = inode_peek_iversion_raw(inode);
+        for (;;) {
+                /* If flag is clear then we needn't do anything */
+                if (!force && !(cur & I_VERSION_QUERIED))
+                        return false;
+
+                /* Since lowest bit is flag, add 2 to avoid it */
+                new = (cur & ~I_VERSION_QUERIED) + I_VERSION_INCREMENT;
+
+                old = atomic64_cmpxchg(&inode->i_version, cur, new);
+                if (likely(old == cur))
+                        break;
+                cur = old;
+        }
+        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_iversion_need_inc - is the i_version in need of being incremented?
+ * @inode: inode to check
+ *
+ * Returns whether the inode->i_version counter needs incrementing on the next
+ * change. Just fetch the value and check the QUERIED flag.
+ */
+static inline bool
+inode_iversion_need_inc(struct inode *inode)
+{
+        return inode_peek_iversion_raw(inode) & I_VERSION_QUERIED;
+}
+
+/**
+ * inode_inc_iversion_raw - forcibly increment raw i_version
+ * @inode: inode that needs to be updated
+ *
+ * Forcbily increment the raw i_version field. This always results in a change
+ * to the raw value.
+ *
+ * NFS will use the i_version field to store the value from the server. It
+ * mostly treats it as opaque, but in the case where it holds a write
+ * delegation, it must increment the value itself. This function does that.
+ */
+static inline void
+inode_inc_iversion_raw(struct inode *inode)
+{
+        atomic64_inc(&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) >> I_VERSION_QUERIED_SHIFT;
+}
+
+/**
+ * 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.
+ *
+ * In this implementation, we fetch the current value, set the QUERIED flag and
+ * then try to swap it into place with a cmpxchg, if it wasn't already set. If
+ * that fails, we try again with the newly fetched value from the cmpxchg.
+ */
+static inline u64
+inode_query_iversion(struct inode *inode)
+{
+        u64 cur, old, new;
+
+        cur = inode_peek_iversion_raw(inode);
+        for (;;) {
+                /* If flag is already set, then no need to swap */
+                if (cur & I_VERSION_QUERIED) {
+                        /*
+                         * This barrier (and the implicit barrier in the
+                         * cmpxchg below) pairs with the barrier in
+                         * inode_maybe_inc_iversion().
+                         */
+                        smp_mb();
+                        break;
+                }
+
+                new = cur | I_VERSION_QUERIED;
+                old = atomic64_cmpxchg(&inode->i_version, cur, new);
+                if (likely(old == cur))
+                        break;
+                cur = old;
+        }
+        return cur >> I_VERSION_QUERIED_SHIFT;
+}
+
+/**
+ * inode_eq_iversion_raw - check whether the raw i_version counter has changed
+ * @inode: inode to check
+ * @old: old value to check against its i_version
+ *
+ * Compare the current raw i_version counter with a previous one. Returns true
+ * if they are the same or false if they are different.
+ */
+static inline bool
+inode_eq_iversion_raw(const struct inode *inode, u64 old)
+{
+        return inode_peek_iversion_raw(inode) == old;
+}
+
+/**
+ * inode_eq_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 true if they are
+ * the same, and false if they are different.
+ *
+ * Note that we don't need to set the QUERIED flag in this case, as the value
+ * in the inode is not being recorded for later use.
+ */
+static inline bool
+inode_eq_iversion(const struct inode *inode, u64 old)
+{
+        return inode_peek_iversion(inode) == old;
+}
+#endif