1ARCHIVE_WRITE_DISK(3) BSD Library Functions Manual ARCHIVE_WRITE_DISK(3)
2
4 archive_write_disk_new, archive_write_disk_set_options,
5 archive_write_disk_set_skip_file, archive_write_disk_set_group_lookup,
6 archive_write_disk_set_standard_lookup,
7 archive_write_disk_set_user_lookup — functions for creating objects on
8 disk
9
11 Streaming Archive Library (libarchive, -larchive)
12
14 #include <archive.h>
15 struct archive *
17 archive_write_disk_new(void);
18 int
20 archive_write_disk_set_options(struct archive *, int flags);
21 int
23 archive_write_disk_set_skip_file(struct archive *, dev_t, ino_t);
24 int
26 archive_write_disk_set_group_lookup(struct archive *, void *,
27 gid_t (*)(void *, const char *gname, gid_t gid),
28 void (*cleanup)(void *));
29 int
31 archive_write_disk_set_standard_lookup(struct archive *);
32 int
34 archive_write_disk_set_user_lookup(struct archive *, void *,
35 uid_t (*)(void *, const char *uname, uid_t uid),
36 void (*cleanup)(void *));
37
39 These functions provide a complete API for creating objects on disk from
40 struct archive_entry descriptions. They are most naturally used when
41 extracting objects from an archive using the archive_read() interface.
42 The general process is to read struct archive_entry objects from an ar‐
43 chive, then write those objects to a struct archive object created using
44 the archive_write_disk() family functions. This interface is deliber‐
45 ately very similar to the archive_write() interface used to write objects
46 to a streaming archive.
47 archive_write_disk_new()
49 Allocates and initializes a struct archive object suitable for
50 writing objects to disk.
51 archive_write_disk_set_skip_file()
53 Records the device and inode numbers of a file that should not be
54 overwritten. This is typically used to ensure that an extraction
55 process does not overwrite the archive from which objects are
56 being read. This capability is technically unnecessary but can
57 be a significant performance optimization in practice.
58 archive_write_disk_set_options()
60 The options field consists of a bitwise OR of one or more of the
61 following values:
62 ARCHIVE_EXTRACT_ACL
63 Attempt to restore Access Control Lists. By default,
64 extended ACLs are ignored.
65 ARCHIVE_EXTRACT_CLEAR_NOCHANGE_FFLAGS
66 Before removing a file system object prior to replacing
67 it, clear platform-specific file flags which might pre‐
68 vent its removal.
69 ARCHIVE_EXTRACT_FFLAGS
70 Attempt to restore file attributes (file flags). By
71 default, file attributes are ignored. See chattr(1)
72 (Linux) or chflags(1) (FreeBSD, Mac OS X) for more infor‐
73 mation on file attributes.
74 ARCHIVE_EXTRACT_MAC_METADATA
75 Mac OS X specific. Restore metadata using copyfile(3).
76 By default, copyfile(3) metadata is ignored.
77 ARCHIVE_EXTRACT_NO_OVERWRITE
78 Existing files on disk will not be overwritten. By
79 default, existing regular files are truncated and over‐
80 written; existing directories will have their permissions
81 updated; other pre-existing objects are unlinked and
82 recreated from scratch.
83 ARCHIVE_EXTRACT_OWNER
84 The user and group IDs should be set on the restored
85 file. By default, the user and group IDs are not
86 restored.
87 ARCHIVE_EXTRACT_PERM
88 Full permissions (including SGID, SUID, and sticky bits)
89 should be restored exactly as specified, without obeying
90 the current umask. Note that SUID and SGID bits can only
91 be restored if the user and group ID of the object on
92 disk are correct. If ARCHIVE_EXTRACT_OWNER is not speci‐
93 fied, then SUID and SGID bits will only be restored if
94 the default user and group IDs of newly-created objects
95 on disk happen to match those specified in the archive
96 entry. By default, only basic permissions are restored,
97 and umask is obeyed.
98 ARCHIVE_EXTRACT_SAFE_WRITES
99 Extract files atomically, by first creating a unique tem‐
100 porary file and then renaming it to its required destina‐
101 tion name. This avoids a race where an application might
102 see a partial file (or no file) during extraction.
103 ARCHIVE_EXTRACT_SECURE_NOABSOLUTEPATHS
104 Refuse to extract an absolute path. The default is to
105 not refuse such paths.
106 ARCHIVE_EXTRACT_SECURE_NODOTDOT
107 Refuse to extract a path that contains a .. element any‐
108 where within it. The default is to not refuse such
109 paths. Note that paths ending in .. always cause an
110 error, regardless of this flag.
111 ARCHIVE_EXTRACT_SECURE_SYMLINKS
112 Refuse to extract any object whose final location would
113 be altered by a symlink on disk. This is intended to
114 help guard against a variety of mischief caused by ar‐
115 chives that (deliberately or otherwise) extract files
116 outside of the current directory. The default is not to
117 perform this check. If
118 ARCHIVE_EXTRACT_SPARSE
119 Scan data for blocks of NUL bytes and try to recreate
120 them with holes. This results in sparse files, indepen‐
121 dent of whether the archive format supports or uses them.
122 ARCHIVE_EXTRACT_UNLINK is specified together with this
123 option, the library will remove any intermediate symlinks
124 it finds and return an error only if such symlink could
125 not be removed.
126 ARCHIVE_EXTRACT_TIME
127 The timestamps (mtime, ctime, and atime) should be
128 restored. By default, they are ignored. Note that
129 restoring of atime is not currently supported.
130 ARCHIVE_EXTRACT_UNLINK
131 Existing files on disk will be unlinked before any
132 attempt to create them. In some cases, this can prove to
133 be a significant performance improvement. By default,
134 existing files are truncated and rewritten, but the file
135 is not recreated. In particular, the default behavior
136 does not break existing hard links.
137 ARCHIVE_EXTRACT_XATTR
138 Attempt to restore extended file attributes. By default,
139 they are ignored. See xattr(7) (Linux), xattr(2) (Mac OS
140 X), or getextattr(8) (FreeBSD) for more information on
141 extended file attributes.
142 archive_write_disk_set_group_lookup(),
144 archive_write_disk_set_user_lookup()
145 The struct archive_entry objects contain both names and ids that
146 can be used to identify users and groups. These names and ids
147 describe the ownership of the file itself and also appear in ACL
148 lists. By default, the library uses the ids and ignores the
149 names, but this can be overridden by registering user and group
150 lookup functions. To register, you must provide a lookup func‐
151 tion which accepts both a name and id and returns a suitable id.
152 You may also provide a void * pointer to a private data structure
153 and a cleanup function for that data. The cleanup function will
154 be invoked when the struct archive object is destroyed.
155 archive_write_disk_set_standard_lookup()
157 This convenience function installs a standard set of user and
158 group lookup functions. These functions use getpwnam(3) and
159 getgrnam(3) to convert names to ids, defaulting to the ids if the
160 names cannot be looked up. These functions also implement a sim‐
161 ple memory cache to reduce the number of calls to getpwnam(3) and
162 getgrnam(3).
163 More information about the struct archive object and the overall design
164 of the library can be found in the libarchive(3) overview. Many of these
165 functions are also documented under archive_write(3).
166
168 Most functions return ARCHIVE_OK (zero) on success, or one of several
169 non-zero error codes for errors. Specific error codes include:
170 ARCHIVE_RETRY for operations that might succeed if retried, ARCHIVE_WARN
171 for unusual conditions that do not prevent further operations, and
172 ARCHIVE_FATAL for serious errors that make remaining operations impossi‐
173 ble.
174 archive_write_disk_new() returns a pointer to a newly-allocated struct
176 archive object.
177 archive_write_data() returns a count of the number of bytes actually
179 written, or -1 on error.
180
182 Detailed error codes and textual descriptions are available from the
183 archive_errno() and archive_error_string() functions.
184
186 tar(1), archive_read(3), archive_write(3), libarchive(3)
187
189 The libarchive library first appeared in FreeBSD 5.3. The
190 archive_write_disk interface was added to libarchive 2.0 and first
191 appeared in FreeBSD 6.3.
192
194 The libarchive library was written by Tim Kientzle <kientzle@acm.org>.
195
197 Directories are actually extracted in two distinct phases. Directories
198 are created during archive_write_header(), but final permissions are not
199 set until archive_write_close(). This separation is necessary to cor‐
200 rectly handle borderline cases such as a non-writable directory contain‐
201 ing files, but can cause unexpected results. In particular, directory
202 permissions are not fully restored until the archive is closed. If you
203 use chdir(2) to change the current directory between calls to
204 archive_read_extract() or before calling archive_read_close(), you may
205 confuse the permission-setting logic with the result that directory per‐
206 missions are restored incorrectly.
207 The library attempts to create objects with filenames longer than
209 PATH_MAX by creating prefixes of the full path and changing the current
210 directory. Currently, this logic is limited in scope; the fixup pass
211 does not work correctly for such objects and the symlink security check
212 option disables the support for very long pathnames.
213 Restoring the path aa/../bb does create each intermediate directory. In
215 particular, the directory aa is created as well as the final object bb.
216 In theory, this can be exploited to create an entire directory hierarchy
217 with a single request. Of course, this does not work if the
218 ARCHIVE_EXTRACT_NODOTDOT option is specified.
219 Implicit directories are always created obeying the current umask.
221 Explicit objects are created obeying the current umask unless
222 ARCHIVE_EXTRACT_PERM is specified, in which case they current umask is
223 ignored.
224 SGID and SUID bits are restored only if the correct user and group could
226 be set. If ARCHIVE_EXTRACT_OWNER is not specified, then no attempt is
227 made to set the ownership. In this case, SGID and SUID bits are restored
228 only if the user and group of the final object happen to match those
229 specified in the entry.
230 The “standard” user-id and group-id lookup functions are not the defaults
232 because getgrnam(3) and getpwnam(3) are sometimes too large for particu‐
233 lar applications. The current design allows the application author to
234 use a more compact implementation when appropriate.
235 There should be a corresponding archive_read_disk interface that walks a
237 directory hierarchy and returns archive entry objects.
238BSD January 19, 2020 BSD