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Commit ad0af710 authored by Amir Goldstein's avatar Amir Goldstein Committed by Miklos Szeredi
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vfs: introduce inode 'inuse' lock 



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: default avatarAmir Goldstein <amir73il@gmail.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
parent 04a01ac7

fs/overlayfs/overlayfs.h

+2 −0
Original line number Diff line number Diff line
@@ -220,6 +220,8 @@ int ovl_check_setxattr(struct dentry *dentry, struct dentry *upperdentry, 
int ovl_set_impure(struct dentry *dentry, struct dentry *upperdentry);

void ovl_set_flag(unsigned long flag, struct inode *inode);

bool ovl_test_flag(unsigned long flag, struct inode *inode);

bool ovl_inuse_trylock(struct dentry *dentry);

void ovl_inuse_unlock(struct dentry *dentry);



static inline bool ovl_is_impuredir(struct dentry *dentry)

{

fs/overlayfs/util.c

+31 −0
Original line number Diff line number Diff line
@@ -347,3 +347,34 @@ bool ovl_test_flag(unsigned long flag, struct inode *inode) 
{

	return test_bit(flag, &OVL_I(inode)->flags);

}



/**

 * Caller must hold a reference to inode to prevent it from being freed while

 * it is marked inuse.

 */

bool ovl_inuse_trylock(struct dentry *dentry)

{

	struct inode *inode = d_inode(dentry);

	bool locked = false;



	spin_lock(&inode->i_lock);

	if (!(inode->i_state & I_OVL_INUSE)) {

		inode->i_state |= I_OVL_INUSE;

		locked = true;

	}

	spin_unlock(&inode->i_lock);



	return locked;

}



void ovl_inuse_unlock(struct dentry *dentry)

{

	if (dentry) {

		struct inode *inode = d_inode(dentry);



		spin_lock(&inode->i_lock);

		WARN_ON(!(inode->i_state & I_OVL_INUSE));

		inode->i_state &= ~I_OVL_INUSE;

		spin_unlock(&inode->i_lock);

	}

}

include/linux/fs.h

+4 −0
Original line number Diff line number Diff line
@@ -1930,6 +1930,9 @@ 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_OVL_INUSE		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)
@@ -1950,6 +1953,7 @@ 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_OVL_INUSE			(1 << 14)



#define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)

#define I_DIRTY_ALL (I_DIRTY | I_DIRTY_TIME)