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df038819 | 1 | /* |
ab5be9fa | 2 | * Copyright (C) 2018 Jérémie Galarneau <jeremie.galarneau@efficios.com> |
df038819 | 3 | * |
ab5be9fa | 4 | * SPDX-License-Identifier: GPL-2.0-only |
df038819 | 5 | * |
df038819 JG |
6 | */ |
7 | ||
8 | #ifndef FD_TRACKER_H | |
9 | #define FD_TRACKER_H | |
10 | ||
f7c3ffd7 | 11 | #include <common/compat/directory-handle.h> |
938bd422 | 12 | #include <common/macros.h> |
df038819 JG |
13 | #include <stdint.h> |
14 | #include <sys/types.h> | |
15 | ||
16 | struct fs_handle; | |
17 | struct fd_tracker; | |
18 | ||
19 | /* | |
20 | * Callback which returns a file descriptor to track through the fd | |
21 | * tracker. This callback must not make use of the fd_tracker as a deadlock | |
22 | * may occur. | |
23 | * | |
24 | * The int pointer argument is an output parameter that should be used to return | |
25 | * the advertised number of file descriptors. | |
26 | * | |
27 | * Must return zero on success. Negative values should map to a UNIX error code. | |
28 | */ | |
29 | typedef int (*fd_open_cb)(void *, int *out_fds); | |
30 | ||
31 | /* | |
32 | * Callback to allow the user to close a now-untracked file descriptor. This | |
33 | * callback must not make use of the fd_tracker as a deadlock may occur. | |
34 | * | |
35 | * The callback can freely modify the in_fds argument as it is copied by the | |
36 | * fd_tracker before being used. The fd tracker assumes in_fds to be closed by | |
37 | * the time the callback returns. | |
38 | * | |
39 | * Must return zero on success. Negative values should map to a UNIX error code. | |
40 | */ | |
41 | typedef int (*fd_close_cb)(void *, int *in_fds); | |
42 | ||
43 | /* | |
44 | * Set the maximal number of fds that the process should be allowed to open at | |
45 | * any given time. This function must be called before any other of this | |
46 | * interface. | |
f7c3ffd7 JG |
47 | * |
48 | * The unlinked_file_path is an absolute path (which does not need to exist) | |
49 | * under which unlinked files will be stored for as long as a reference to them | |
50 | * is held. | |
df038819 | 51 | */ |
938bd422 | 52 | LTTNG_HIDDEN |
f7c3ffd7 JG |
53 | struct fd_tracker *fd_tracker_create(const char *unlinked_file_path, |
54 | unsigned int capacity); | |
df038819 JG |
55 | |
56 | /* Returns an error if file descriptors are leaked. */ | |
938bd422 | 57 | LTTNG_HIDDEN |
df038819 JG |
58 | int fd_tracker_destroy(struct fd_tracker *tracker); |
59 | ||
60 | /* | |
61 | * Open a handle to a suspendable filesystem file descriptor. | |
62 | * | |
63 | * See OPEN(3) for an explanation of flags and mode. NULL is returned in case of | |
64 | * error and errno is left untouched. Note that passing NULL as mode will result | |
65 | * in open()'s default behaviour being used (using the process' umask). | |
66 | * | |
67 | * A fs_handle wraps a file descriptor created by OPEN(3). It is suspendable | |
68 | * meaning that the underlying file may be closed at any time unless the | |
69 | * handle is marked as being in-use (see fs_handle_get_fd() and | |
70 | * fs_handle_put_fd()). | |
71 | * | |
72 | * If the tracker opted to close the underlying file descriptor, it will | |
73 | * be restored to its last known state when it is obtained through | |
74 | * the fs_handle's fs_handle_get_fd() method. | |
75 | * | |
76 | * Note that a suspendable file descriptor can be closed by the fd tracker at | |
77 | * anytime when it is not in use. This means that the user should not rely on it | |
78 | * being safe to unlink the file. Moreover, concurent modifications to the file | |
79 | * (e.g. truncation) may react differently than if the file descriptor was kept | |
80 | * open. | |
81 | */ | |
938bd422 | 82 | LTTNG_HIDDEN |
df038819 | 83 | struct fs_handle *fd_tracker_open_fs_handle(struct fd_tracker *tracker, |
f7c3ffd7 | 84 | struct lttng_directory_handle *directory, |
5c1f54d1 JG |
85 | const char *path, |
86 | int flags, | |
87 | mode_t *mode); | |
df038819 JG |
88 | |
89 | /* | |
90 | * Open a tracked unsuspendable file descriptor. | |
91 | * | |
92 | * This function allows the fd tracker to keep track of unsuspendable | |
93 | * file descriptors. A callback, open, is passed to allow the tracker | |
94 | * to atomically reserve an entry for a given count of new file descriptors, | |
95 | * suspending file descriptors as needed, and invoke the provided callback | |
96 | * without ever exceeding the tracker's capacity. | |
97 | * | |
98 | * fd_count indicates the count of file descriptors that will be opened and | |
99 | * returned by the open callback. The storage location at out_fds is assumed | |
100 | * to be large enough to hold 'fd_count * sizeof(int)'. | |
101 | * | |
102 | * Names may be provided to allow easier debugging of file descriptor | |
103 | * exhaustions. | |
104 | * | |
105 | * The callback's return value is returned to the user. Additionally, two | |
106 | * negative tracker-specific codes may be returned: | |
107 | * - ENOMEM: allocation of a new entry failed, | |
108 | * - EMFILE: too many unsuspendable fds are opened and the tracker can't | |
d49487dc | 109 | * accommodates the request for a new unsuspendable entry. |
df038819 | 110 | */ |
938bd422 | 111 | LTTNG_HIDDEN |
df038819 | 112 | int fd_tracker_open_unsuspendable_fd(struct fd_tracker *tracker, |
5c1f54d1 JG |
113 | int *out_fds, |
114 | const char **names, | |
115 | unsigned int fd_count, | |
116 | fd_open_cb open, | |
117 | void *data); | |
df038819 JG |
118 | |
119 | /* | |
120 | * Close a tracked unsuspendable file descriptor. | |
121 | * | |
122 | * This function allows the fd tracker to keep track of unsuspendable | |
123 | * file descriptors. A callback, close, is passed to allow the tracker | |
124 | * to atomically release a file descriptor entry. | |
125 | * | |
126 | * Returns 0 if the close callback returned success. Returns the value returned | |
127 | * by the close callback if it is negative. Additionally, a tracker-specific | |
128 | * code may be returned: | |
129 | * - EINVAL: a file descriptor was unknown to the tracker | |
130 | * | |
131 | * Closed fds are set to -1 in the fds array which, in the event of an error, | |
132 | * allows the user to know which file descriptors are no longer being tracked. | |
133 | */ | |
938bd422 | 134 | LTTNG_HIDDEN |
df038819 | 135 | int fd_tracker_close_unsuspendable_fd(struct fd_tracker *tracker, |
5c1f54d1 JG |
136 | int *fds, |
137 | unsigned int fd_count, | |
138 | fd_close_cb close, | |
df038819 JG |
139 | void *data); |
140 | ||
141 | /* | |
142 | * Log the contents of the fd_tracker. | |
143 | */ | |
938bd422 | 144 | LTTNG_HIDDEN |
df038819 JG |
145 | void fd_tracker_log(struct fd_tracker *tracker); |
146 | ||
147 | /* | |
148 | * Marks the handle as the most recently used and marks the 'fd' as | |
149 | * "in-use". This prevents the tracker from recycling the underlying | |
150 | * file descriptor while it is actively being used by a thread. | |
151 | * | |
152 | * Don't forget that the tracker may be initiating an fd 'suspension' | |
153 | * from another thread as the need to free an fd slot may arise from any | |
154 | * thread within the daemon. | |
155 | * | |
156 | * Note that a restorable fd should never be held for longer than | |
157 | * strictly necessary (e.g. the duration of a syscall()). | |
158 | * | |
159 | * Returns the fd on success, otherwise a negative value may be returned | |
160 | * if the restoration of the fd failed. | |
161 | */ | |
938bd422 | 162 | LTTNG_HIDDEN |
df038819 JG |
163 | int fs_handle_get_fd(struct fs_handle *handle); |
164 | ||
165 | /* | |
166 | * Used by the application to signify that it is no longer using the | |
167 | * underlying fd and that it may be suspended. | |
168 | */ | |
938bd422 | 169 | LTTNG_HIDDEN |
df038819 JG |
170 | void fs_handle_put_fd(struct fs_handle *handle); |
171 | ||
9d16fc7f JG |
172 | /* |
173 | * Unlink the file associated to an fs_handle. Note that the unlink | |
174 | * operation will not be performed immediately. It will only be performed | |
175 | * once all references to the underlying file (through other fs_handle objects) | |
176 | * have been released. | |
177 | * | |
178 | * However, note that the file will be renamed so as to provide the observable | |
179 | * effect of an unlink(), that is removing a name from the filesystem. | |
180 | * | |
181 | * Returns 0 on success, otherwise a negative value will be returned | |
182 | * if the operation failed. | |
183 | */ | |
938bd422 | 184 | LTTNG_HIDDEN |
9d16fc7f JG |
185 | int fs_handle_unlink(struct fs_handle *handle); |
186 | ||
df038819 JG |
187 | /* |
188 | * Frees the handle and discards the underlying fd. | |
189 | */ | |
938bd422 | 190 | LTTNG_HIDDEN |
df038819 JG |
191 | int fs_handle_close(struct fs_handle *handle); |
192 | ||
193 | #endif /* FD_TRACKER_H */ |