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Currently, __debugfs_create_file allocates one struct debugfs_fsdata instance for every file created. However, there are potentially many debugfs file around, most of which are never touched by userspace. Thus, defer the allocations to the first usage, i.e. to the first debugfs_file_get(). A dentry's ->d_fsdata starts out to point to the "real", user provided fops. After a debugfs_fsdata instance has been allocated (and the real fops pointer has been moved over into its ->real_fops member), ->d_fsdata is changed to point to it from then on. The two cases are distinguished by setting BIT(0) for the real fops case. struct debugfs_fsdata's foremost purpose is to track active users and to make debugfs_remove() block until they are done. Since no debugfs_fsdata instance means no active users, make debugfs_remove() return immediately in this case. Take care of possible races between debugfs_file_get() and debugfs_remove(): either debugfs_remove() must see a debugfs_fsdata instance and thus wait for possible active users or debugfs_file_get() must see a dead dentry and return immediately. Make a dentry's ->d_release(), i.e. debugfs_release_dentry(), check whether ->d_fsdata is actually a debugfs_fsdata instance before kfree()ing it. Similarly, make debugfs_real_fops() check whether ->d_fsdata is actually a debugfs_fsdata instance before returning it, otherwise emit a warning. The set of possible error codes returned from debugfs_file_get() has grown from -EIO to -EIO and -ENOMEM. Make open_proxy_open() and full_proxy_open() pass the -ENOMEM onwards to their callers. Signed-off-by: Nicolai Stange <nicstange@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
36 lines
1.1 KiB
C
36 lines
1.1 KiB
C
/*
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* internal.h - declarations internal to debugfs
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*
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* Copyright (C) 2016 Nicolai Stange <nicstange@gmail.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License version
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* 2 as published by the Free Software Foundation.
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*
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*/
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#ifndef _DEBUGFS_INTERNAL_H_
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#define _DEBUGFS_INTERNAL_H_
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struct file_operations;
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/* declared over in file.c */
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extern const struct file_operations debugfs_noop_file_operations;
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extern const struct file_operations debugfs_open_proxy_file_operations;
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extern const struct file_operations debugfs_full_proxy_file_operations;
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struct debugfs_fsdata {
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const struct file_operations *real_fops;
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refcount_t active_users;
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struct completion active_users_drained;
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};
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/*
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* A dentry's ->d_fsdata either points to the real fops or to a
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* dynamically allocated debugfs_fsdata instance.
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* In order to distinguish between these two cases, a real fops
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* pointer gets its lowest bit set.
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*/
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#define DEBUGFS_FSDATA_IS_REAL_FOPS_BIT BIT(0)
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#endif /* _DEBUGFS_INTERNAL_H_ */
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