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dentry name snapshots 

take_dentry_name_snapshot() takes a safe snapshot of dentry name;
if the name is a short one, it gets copied into caller-supplied
structure, otherwise an extra reference to external name is grabbed
(those are never modified). In either case the pointer to stable
string is stored into the same structure.

dentry must be held by the caller of take_dentry_name_snapshot(),
but may be freely dropped afterwards - the snapshot will stay
until destroyed by release_dentry_name_snapshot().

Intended use:
	struct name_snapshot s;

	take_dentry_name_snapshot(&s, dentry);
	...
	access s.name
	...
	release_dentry_name_snapshot(&s);

Replaces fsnotify_oldname_...(), gets used in fsnotify to obtain the name
to pass down with event.

Git-repo: https://github.com/torvalds/linux.git
Git-commit: 49d31c2f389acfe83417083e1208422b4091cd9e
Change-Id: I295c55a104c12150356a027dd37ff3af7fee13e0
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ankit Jain <jankit@codeaurora.org>
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>
This commit is contained in:
Al Viro 2017-07-07 14:51:19 -04:00 committed by syphyr
parent 9466b3f669
commit ded010f7fb
1 changed files with 27 additions and 36 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

63
fs/dcache.c
View File

@ -268,42 +268,6 @@ static void d_free(struct dentry *dentry)
dentry_free(dentry);
}
void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
{
spin_lock(&dentry->d_lock);
if (unlikely(dname_external(dentry))) {
u32 len;
char *p = NULL;
do {
len = dentry->d_name.len;
spin_unlock(&dentry->d_lock);
if (p)
kfree(p);
p = kmalloc(len + 1, GFP_KERNEL | __GFP_NOFAIL);
spin_lock(&dentry->d_lock);
} while (dentry->d_name.len > len);
memcpy(p, dentry->d_name.name, dentry->d_name.len + 1);
spin_unlock(&dentry->d_lock);
name->name = p;
} else {
memcpy(name->inline_name, dentry->d_iname, DNAME_INLINE_LEN);
spin_unlock(&dentry->d_lock);
name->name = name->inline_name;
}
}
EXPORT_SYMBOL(take_dentry_name_snapshot);
void release_dentry_name_snapshot(struct name_snapshot *name)
{
if (unlikely(name->name != name->inline_name))
kfree(name->name);
}
EXPORT_SYMBOL(release_dentry_name_snapshot);
/**
* dentry_rcuwalk_barrier - invalidate in-progress rcu-walk lookups
* @dentry: the target dentry
@ -366,6 +330,33 @@ static void dentry_unlink_inode(struct dentry * dentry)
iput(inode);
}
void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
{
spin_lock(&dentry->d_lock);
if (unlikely(dname_external(dentry))) {
struct external_name *p = external_name(dentry);
atomic_inc(&p->u.count);
spin_unlock(&dentry->d_lock);
name->name = p->name;
} else {
memcpy(name->inline_name, dentry->d_iname, DNAME_INLINE_LEN);
spin_unlock(&dentry->d_lock);
name->name = name->inline_name;
}
}
EXPORT_SYMBOL(take_dentry_name_snapshot);
void release_dentry_name_snapshot(struct name_snapshot *name)
{
if (unlikely(name->name != name->inline_name)) {
struct external_name *p;
p = container_of(name->name, struct external_name, name[0]);
if (unlikely(atomic_dec_and_test(&p->u.count)))
kfree_rcu(p, u.head);
}
}
EXPORT_SYMBOL(release_dentry_name_snapshot);
/*
* dentry_lru_(add|del|prune|move_tail) must be called with d_lock held.
*/