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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 | ||
c9e313bc SM |
11 | #include <common/compat/directory-handle.hpp> |
12 | #include <common/macros.hpp> | |
28f23191 | 13 | |
df038819 JG |
14 | #include <stdint.h> |
15 | #include <sys/types.h> | |
16 | ||
17 | struct fs_handle; | |
18 | struct fd_tracker; | |
19 | ||
20 | /* | |
21 | * Callback which returns a file descriptor to track through the fd | |
22 | * tracker. This callback must not make use of the fd_tracker as a deadlock | |
23 | * may occur. | |
24 | * | |
25 | * The int pointer argument is an output parameter that should be used to return | |
26 | * the advertised number of file descriptors. | |
27 | * | |
28 | * Must return zero on success. Negative values should map to a UNIX error code. | |
29 | */ | |
e665dfbc | 30 | using fd_open_cb = int (*)(void *, int *); |
df038819 JG |
31 | |
32 | /* | |
33 | * Callback to allow the user to close a now-untracked file descriptor. This | |
34 | * callback must not make use of the fd_tracker as a deadlock may occur. | |
35 | * | |
36 | * The callback can freely modify the in_fds argument as it is copied by the | |
37 | * fd_tracker before being used. The fd tracker assumes in_fds to be closed by | |
38 | * the time the callback returns. | |
39 | * | |
40 | * Must return zero on success. Negative values should map to a UNIX error code. | |
41 | */ | |
e665dfbc | 42 | using fd_close_cb = int (*)(void *, int *); |
df038819 JG |
43 | |
44 | /* | |
45 | * Set the maximal number of fds that the process should be allowed to open at | |
46 | * any given time. This function must be called before any other of this | |
47 | * interface. | |
f7c3ffd7 JG |
48 | * |
49 | * The unlinked_file_path is an absolute path (which does not need to exist) | |
50 | * under which unlinked files will be stored for as long as a reference to them | |
51 | * is held. | |
df038819 | 52 | */ |
28f23191 | 53 | struct fd_tracker *fd_tracker_create(const char *unlinked_file_path, unsigned int capacity); |
df038819 JG |
54 | |
55 | /* Returns an error if file descriptors are leaked. */ | |
56 | int fd_tracker_destroy(struct fd_tracker *tracker); | |
57 | ||
58 | /* | |
59 | * Open a handle to a suspendable filesystem file descriptor. | |
60 | * | |
61 | * See OPEN(3) for an explanation of flags and mode. NULL is returned in case of | |
62 | * error and errno is left untouched. Note that passing NULL as mode will result | |
63 | * in open()'s default behaviour being used (using the process' umask). | |
64 | * | |
65 | * A fs_handle wraps a file descriptor created by OPEN(3). It is suspendable | |
66 | * meaning that the underlying file may be closed at any time unless the | |
67 | * handle is marked as being in-use (see fs_handle_get_fd() and | |
68 | * fs_handle_put_fd()). | |
69 | * | |
70 | * If the tracker opted to close the underlying file descriptor, it will | |
71 | * be restored to its last known state when it is obtained through | |
72 | * the fs_handle's fs_handle_get_fd() method. | |
73 | * | |
74 | * Note that a suspendable file descriptor can be closed by the fd tracker at | |
75 | * anytime when it is not in use. This means that the user should not rely on it | |
76 | * being safe to unlink the file. Moreover, concurent modifications to the file | |
77 | * (e.g. truncation) may react differently than if the file descriptor was kept | |
78 | * open. | |
79 | */ | |
80 | struct fs_handle *fd_tracker_open_fs_handle(struct fd_tracker *tracker, | |
28f23191 JG |
81 | struct lttng_directory_handle *directory, |
82 | const char *path, | |
83 | int flags, | |
84 | mode_t *mode); | |
df038819 JG |
85 | |
86 | /* | |
87 | * Open a tracked unsuspendable file descriptor. | |
88 | * | |
89 | * This function allows the fd tracker to keep track of unsuspendable | |
90 | * file descriptors. A callback, open, is passed to allow the tracker | |
91 | * to atomically reserve an entry for a given count of new file descriptors, | |
92 | * suspending file descriptors as needed, and invoke the provided callback | |
93 | * without ever exceeding the tracker's capacity. | |
94 | * | |
95 | * fd_count indicates the count of file descriptors that will be opened and | |
96 | * returned by the open callback. The storage location at out_fds is assumed | |
97 | * to be large enough to hold 'fd_count * sizeof(int)'. | |
98 | * | |
99 | * Names may be provided to allow easier debugging of file descriptor | |
100 | * exhaustions. | |
101 | * | |
102 | * The callback's return value is returned to the user. Additionally, two | |
103 | * negative tracker-specific codes may be returned: | |
104 | * - ENOMEM: allocation of a new entry failed, | |
105 | * - EMFILE: too many unsuspendable fds are opened and the tracker can't | |
d49487dc | 106 | * accommodates the request for a new unsuspendable entry. |
df038819 JG |
107 | */ |
108 | int fd_tracker_open_unsuspendable_fd(struct fd_tracker *tracker, | |
28f23191 JG |
109 | int *out_fds, |
110 | const char **names, | |
111 | unsigned int fd_count, | |
112 | fd_open_cb open, | |
113 | void *data); | |
df038819 JG |
114 | |
115 | /* | |
116 | * Close a tracked unsuspendable file descriptor. | |
117 | * | |
118 | * This function allows the fd tracker to keep track of unsuspendable | |
119 | * file descriptors. A callback, close, is passed to allow the tracker | |
120 | * to atomically release a file descriptor entry. | |
121 | * | |
122 | * Returns 0 if the close callback returned success. Returns the value returned | |
123 | * by the close callback if it is negative. Additionally, a tracker-specific | |
124 | * code may be returned: | |
125 | * - EINVAL: a file descriptor was unknown to the tracker | |
126 | * | |
127 | * Closed fds are set to -1 in the fds array which, in the event of an error, | |
128 | * allows the user to know which file descriptors are no longer being tracked. | |
129 | */ | |
28f23191 JG |
130 | int fd_tracker_close_unsuspendable_fd( |
131 | struct fd_tracker *tracker, int *fds, unsigned int fd_count, fd_close_cb close, void *data); | |
df038819 JG |
132 | |
133 | /* | |
134 | * Log the contents of the fd_tracker. | |
135 | */ | |
136 | void fd_tracker_log(struct fd_tracker *tracker); | |
137 | ||
df038819 | 138 | #endif /* FD_TRACKER_H */ |