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dentry name snapshots

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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.

Signed-off-by: Al Viro <[email protected]>
This commit is contained in:
Al Viro 2017-07-07 14:51:19 -04:00
commit 49d31c2f38
6 changed files with 48 additions and 42 deletions
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8
fs/namei.c
View file

@ -4362,11 +4362,11 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
{
int error;
bool is_dir = d_is_dir(old_dentry);
const unsigned char *old_name;
struct inode *source = old_dentry->d_inode;
struct inode *target = new_dentry->d_inode;
bool new_is_dir = false;
unsigned max_links = new_dir->i_sb->s_max_links;
struct name_snapshot old_name;
if (source == target)
return 0;
@ -4413,7 +4413,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
if (error)
return error;
old_name = fsnotify_oldname_init(old_dentry->d_name.name);
take_dentry_name_snapshot(&old_name, old_dentry);
dget(new_dentry);
if (!is_dir || (flags & RENAME_EXCHANGE))
lock_two_nondirectories(source, target);
@ -4468,14 +4468,14 @@ out:
inode_unlock(target);
dput(new_dentry);
if (!error) {
fsnotify_move(old_dir, new_dir, old_name, is_dir,
fsnotify_move(old_dir, new_dir, old_name.name, is_dir,
!(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
if (flags & RENAME_EXCHANGE) {
fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,
new_is_dir, NULL, new_dentry);
}
}
fsnotify_oldname_free(old_name);
release_dentry_name_snapshot(&old_name);
return error;
}