Added an i_state flag I_INUSE and helpers to set/clear/test the bit.
The 'inuse' lock is an 'advisory' inode lock, that can be used to extend
exclusive create protection beyond parent->i_mutex lock among cooperating
users.
This is going to be used by overlayfs to get exclusive ownership on upper
and work dirs among overlayfs mounts.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/inode.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 14 ++++++++++++++
2 files changed, 64 insertions(+)
diff --git a/fs/inode.c b/fs/inode.c
index db5914783a71..6a41b27467eb 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2120,3 +2120,53 @@ struct timespec current_time(struct inode *inode)
return timespec_trunc(now, inode->i_sb->s_time_gran);
}
EXPORT_SYMBOL(current_time);
+
+/**
+ * inode_inuse_trylock - try to get an exclusive 'inuse' lock on inode
+ * @inode: inode being locked
+ *
+ * The 'inuse' lock is an 'advisory' lock that can be used to extend exclusive
+ * create protection beyond parent->i_mutex lock among cooperating users.
+ * Used by overlayfs to get exclusive ownership on upper and work dirs among
+ * overlayfs mounts.
+ *
+ * Caller must hold a reference to inode to prevent it from being freed while
+ * it is marked inuse.
+ *
+ * Return true if I_INUSE flag was set by this call.
+ */
+bool inode_inuse_trylock(struct inode *inode)
+{
+ bool locked = false;
+
+ spin_lock(&inode->i_lock);
+ if (!WARN_ON(!atomic_read(&inode->i_count)) &&
+ !WARN_ON(inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) &&
+ !(inode->i_state & I_INUSE)) {
+ inode->i_state |= I_INUSE;
+ locked = true;
+ }
+ spin_unlock(&inode->i_lock);
+ return locked;
+}
+EXPORT_SYMBOL(inode_inuse_trylock);
+
+/**
+ * inode_inuse_unlock - release exclusive 'inuse' lock
+ * @inode: inode inuse to unlock
+ *
+ * Clear the I_INUSE state.
+ *
+ * Caller must hold a reference to inode and must have successfully marked
+ * the inode 'inuse' prior to this call.
+ */
+void inode_inuse_unlock(struct inode *inode)
+{
+ spin_lock(&inode->i_lock);
+ WARN_ON(!atomic_read(&inode->i_count));
+ WARN_ON(inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE));
+ WARN_ON(!(inode->i_state & I_INUSE));
+ inode->i_state &= ~I_INUSE;
+ spin_unlock(&inode->i_lock);
+}
+EXPORT_SYMBOL(inode_inuse_unlock);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index aab10f93ef23..532802120258 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1929,6 +1929,12 @@ static inline bool HAS_UNMAPPED_ID(struct inode *inode)
* wb stat updates to grab mapping->tree_lock. See
* inode_switch_wb_work_fn() for details.
*
+ * I_INUSE An 'advisory' bit to get exclusive ownership on inode
+ * using inode_inuse_trylock(). It can be used to extend
+ * exclusive create protection beyond parent->i_mutex lock.
+ * Used by overlayfs to get exclusive ownership on upper
+ * and work dirs among overlayfs mounts.
+ *
* Q: What is the difference between I_WILL_FREE and I_FREEING?
*/
#define I_DIRTY_SYNC (1 << 0)
@@ -1949,6 +1955,7 @@ static inline bool HAS_UNMAPPED_ID(struct inode *inode)
#define __I_DIRTY_TIME_EXPIRED 12
#define I_DIRTY_TIME_EXPIRED (1 << __I_DIRTY_TIME_EXPIRED)
#define I_WB_SWITCH (1 << 13)
+#define I_INUSE (1 << 14)
#define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)
#define I_DIRTY_ALL (I_DIRTY | I_DIRTY_TIME)
@@ -3258,5 +3265,12 @@ static inline bool dir_relax_shared(struct inode *inode)
extern bool path_noexec(const struct path *path);
extern void inode_nohighmem(struct inode *inode);
+extern bool inode_inuse_trylock(struct inode *inode);
+extern void inode_inuse_unlock(struct inode *inode);
+
+static inline bool inode_inuse(struct inode *inode)
+{
+ return inode->i_state & I_INUSE;
+}
#endif /* _LINUX_FS_H */
--
2.7.4
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