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-rw-r--r--Documentation/filesystems/inotify.txt130
1 files changed, 124 insertions, 6 deletions
diff --git a/Documentation/filesystems/inotify.txt b/Documentation/filesystems/inotify.txt
index 6d501903f68e..59a919f16144 100644
--- a/Documentation/filesystems/inotify.txt
+++ b/Documentation/filesystems/inotify.txt
@@ -69,17 +69,135 @@ Prototypes:
69 int inotify_rm_watch (int fd, __u32 mask); 69 int inotify_rm_watch (int fd, __u32 mask);
70 70
71 71
72(iii) Internal Kernel Implementation 72(iii) Kernel Interface
73 73
74Each inotify instance is associated with an inotify_device structure. 74Inotify's kernel API consists a set of functions for managing watches and an
75event callback.
76
77To use the kernel API, you must first initialize an inotify instance with a set
78of inotify_operations. You are given an opaque inotify_handle, which you use
79for any further calls to inotify.
80
81 struct inotify_handle *ih = inotify_init(my_event_handler);
82
83You must provide a function for processing events and a function for destroying
84the inotify watch.
85
86 void handle_event(struct inotify_watch *watch, u32 wd, u32 mask,
87 u32 cookie, const char *name, struct inode *inode)
88
89 watch - the pointer to the inotify_watch that triggered this call
90 wd - the watch descriptor
91 mask - describes the event that occurred
92 cookie - an identifier for synchronizing events
93 name - the dentry name for affected files in a directory-based event
94 inode - the affected inode in a directory-based event
95
96 void destroy_watch(struct inotify_watch *watch)
97
98You may add watches by providing a pre-allocated and initialized inotify_watch
99structure and specifying the inode to watch along with an inotify event mask.
100You must pin the inode during the call. You will likely wish to embed the
101inotify_watch structure in a structure of your own which contains other
102information about the watch. Once you add an inotify watch, it is immediately
103subject to removal depending on filesystem events. You must grab a reference if
104you depend on the watch hanging around after the call.
105
106 inotify_init_watch(&my_watch->iwatch);
107 inotify_get_watch(&my_watch->iwatch); // optional
108 s32 wd = inotify_add_watch(ih, &my_watch->iwatch, inode, mask);
109 inotify_put_watch(&my_watch->iwatch); // optional
110
111You may use the watch descriptor (wd) or the address of the inotify_watch for
112other inotify operations. You must not directly read or manipulate data in the
113inotify_watch. Additionally, you must not call inotify_add_watch() more than
114once for a given inotify_watch structure, unless you have first called either
115inotify_rm_watch() or inotify_rm_wd().
116
117To determine if you have already registered a watch for a given inode, you may
118call inotify_find_watch(), which gives you both the wd and the watch pointer for
119the inotify_watch, or an error if the watch does not exist.
120
121 wd = inotify_find_watch(ih, inode, &watchp);
122
123You may use container_of() on the watch pointer to access your own data
124associated with a given watch. When an existing watch is found,
125inotify_find_watch() bumps the refcount before releasing its locks. You must
126put that reference with:
127
128 put_inotify_watch(watchp);
129
130Call inotify_find_update_watch() to update the event mask for an existing watch.
131inotify_find_update_watch() returns the wd of the updated watch, or an error if
132the watch does not exist.
133
134 wd = inotify_find_update_watch(ih, inode, mask);
135
136An existing watch may be removed by calling either inotify_rm_watch() or
137inotify_rm_wd().
138
139 int ret = inotify_rm_watch(ih, &my_watch->iwatch);
140 int ret = inotify_rm_wd(ih, wd);
141
142A watch may be removed while executing your event handler with the following:
143
144 inotify_remove_watch_locked(ih, iwatch);
145
146Call inotify_destroy() to remove all watches from your inotify instance and
147release it. If there are no outstanding references, inotify_destroy() will call
148your destroy_watch op for each watch.
149
150 inotify_destroy(ih);
151
152When inotify removes a watch, it sends an IN_IGNORED event to your callback.
153You may use this event as an indication to free the watch memory. Note that
154inotify may remove a watch due to filesystem events, as well as by your request.
155If you use IN_ONESHOT, inotify will remove the watch after the first event, at
156which point you may call the final inotify_put_watch.
157
158(iv) Kernel Interface Prototypes
159
160 struct inotify_handle *inotify_init(struct inotify_operations *ops);
161
162 inotify_init_watch(struct inotify_watch *watch);
163
164 s32 inotify_add_watch(struct inotify_handle *ih,
165 struct inotify_watch *watch,
166 struct inode *inode, u32 mask);
167
168 s32 inotify_find_watch(struct inotify_handle *ih, struct inode *inode,
169 struct inotify_watch **watchp);
170
171 s32 inotify_find_update_watch(struct inotify_handle *ih,
172 struct inode *inode, u32 mask);
173
174 int inotify_rm_wd(struct inotify_handle *ih, u32 wd);
175
176 int inotify_rm_watch(struct inotify_handle *ih,
177 struct inotify_watch *watch);
178
179 void inotify_remove_watch_locked(struct inotify_handle *ih,
180 struct inotify_watch *watch);
181
182 void inotify_destroy(struct inotify_handle *ih);
183
184 void get_inotify_watch(struct inotify_watch *watch);
185 void put_inotify_watch(struct inotify_watch *watch);
186
187
188(v) Internal Kernel Implementation
189
190Each inotify instance is represented by an inotify_handle structure.
191Inotify's userspace consumers also have an inotify_device which is
192associated with the inotify_handle, and on which events are queued.
75 193
76Each watch is associated with an inotify_watch structure. Watches are chained 194Each watch is associated with an inotify_watch structure. Watches are chained
77off of each associated device and each associated inode. 195off of each associated inotify_handle and each associated inode.
78 196
79See fs/inotify.c for the locking and lifetime rules. 197See fs/inotify.c and fs/inotify_user.c for the locking and lifetime rules.
80 198
81 199
82(iv) Rationale 200(vi) Rationale
83 201
84Q: What is the design decision behind not tying the watch to the open fd of 202Q: What is the design decision behind not tying the watch to the open fd of
85 the watched object? 203 the watched object?
@@ -145,7 +263,7 @@ A: The poor user-space interface is the second biggest problem with dnotify.
145 file descriptor-based one that allows basic file I/O and poll/select. 263 file descriptor-based one that allows basic file I/O and poll/select.
146 Obtaining the fd and managing the watches could have been done either via a 264 Obtaining the fd and managing the watches could have been done either via a
147 device file or a family of new system calls. We decided to implement a 265 device file or a family of new system calls. We decided to implement a
148 family of system calls because that is the preffered approach for new kernel 266 family of system calls because that is the preferred approach for new kernel
149 interfaces. The only real difference was whether we wanted to use open(2) 267 interfaces. The only real difference was whether we wanted to use open(2)
150 and ioctl(2) or a couple of new system calls. System calls beat ioctls. 268 and ioctl(2) or a couple of new system calls. System calls beat ioctls.
151 269