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8654f9d7 PE |
1 | /* Create /proc/self/fd-related names for subfiles of open directories. |
2 | ||
ba318903 | 3 | Copyright (C) 2006, 2009-2014 Free Software Foundation, Inc. |
8654f9d7 PE |
4 | |
5 | This program is free software: you can redistribute it and/or modify | |
6 | it under the terms of the GNU General Public License as published by | |
7 | the Free Software Foundation; either version 3 of the License, or | |
8 | (at your option) any later version. | |
9 | ||
10 | This program is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | GNU General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU General Public License | |
16 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
17 | ||
18 | /* Written by Paul Eggert. */ | |
19 | ||
20 | #include <config.h> | |
21 | ||
22 | #include "openat-priv.h" | |
23 | ||
24 | #include <sys/types.h> | |
25 | #include <sys/stat.h> | |
26 | #include <fcntl.h> | |
27 | ||
28 | #include <stdio.h> | |
29 | #include <stdlib.h> | |
30 | #include <string.h> | |
31 | #include <unistd.h> | |
32 | ||
33 | #include "intprops.h" | |
34 | ||
8654f9d7 PE |
35 | #define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s" |
36 | ||
37 | #define PROC_SELF_FD_NAME_SIZE_BOUND(len) \ | |
38 | (sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \ | |
39 | + INT_STRLEN_BOUND (int) + (len) + 1) | |
40 | ||
41 | ||
42 | /* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE | |
43 | respectively for %d and %s. If successful, return BUF if the | |
44 | result fits in BUF, dynamically allocated memory otherwise. But | |
45 | return NULL if /proc is not reliable, either because the operating | |
46 | system support is lacking or because memory is low. */ | |
47 | char * | |
48 | openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file) | |
49 | { | |
50 | static int proc_status = 0; | |
51 | ||
52 | /* Make sure the caller gets ENOENT when appropriate. */ | |
53 | if (!*file) | |
54 | { | |
55 | buf[0] = '\0'; | |
56 | return buf; | |
57 | } | |
58 | ||
59 | if (! proc_status) | |
60 | { | |
61 | /* Set PROC_STATUS to a positive value if /proc/self/fd is | |
62 | reliable, and a negative value otherwise. Solaris 10 | |
63 | /proc/self/fd mishandles "..", and any file name might expand | |
64 | to ".." after symbolic link expansion, so avoid /proc/self/fd | |
65 | if it mishandles "..". Solaris 10 has openat, but this | |
66 | problem is exhibited on code that built on Solaris 8 and | |
67 | running on Solaris 10. */ | |
68 | ||
69 | int proc_self_fd = open ("/proc/self/fd", | |
70 | O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK); | |
71 | if (proc_self_fd < 0) | |
72 | proc_status = -1; | |
73 | else | |
74 | { | |
75 | /* Detect whether /proc/self/fd/%i/../fd exists, where %i is the | |
76 | number of a file descriptor open on /proc/self/fd. On Linux, | |
77 | that name resolves to /proc/self/fd, which was opened above. | |
78 | However, on Solaris, it may resolve to /proc/self/fd/fd, which | |
79 | cannot exist, since all names in /proc/self/fd are numeric. */ | |
80 | char dotdot_buf[PROC_SELF_FD_NAME_SIZE_BOUND (sizeof "../fd" - 1)]; | |
81 | sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, "../fd"); | |
82 | proc_status = access (dotdot_buf, F_OK) ? -1 : 1; | |
83 | close (proc_self_fd); | |
84 | } | |
85 | } | |
86 | ||
87 | if (proc_status < 0) | |
88 | return NULL; | |
89 | else | |
90 | { | |
91 | size_t bufsize = PROC_SELF_FD_NAME_SIZE_BOUND (strlen (file)); | |
92 | char *result = buf; | |
93 | if (OPENAT_BUFFER_SIZE < bufsize) | |
94 | { | |
95 | result = malloc (bufsize); | |
96 | if (! result) | |
97 | return NULL; | |
98 | } | |
99 | sprintf (result, PROC_SELF_FD_FORMAT, fd, file); | |
100 | return result; | |
101 | } | |
102 | } |