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, archive_write_header,
8 archive_write_data, archive_write_finish_entry, archive_write_close,
9 archive_write_finish — functions for creating objects on disk
10
12 #include <archive.h>
13 struct archive *
15 archive_write_disk_new(void);
16 int
18 archive_write_disk_set_options(struct archive *, int flags);
19 int
21 archive_write_disk_set_skip_file(struct archive *, dev_t, ino_t);
22 int
24 archive_write_disk_set_group_lookup(struct archive *, void *,
25 gid_t (*)(void *, const char *gname, gid_t gid),
26 void (*cleanup)(void *));
27 int
29 archive_write_disk_set_standard_lookup(struct archive *);
30 int
32 archive_write_disk_set_user_lookup(struct archive *, void *,
33 uid_t (*)(void *, const char *uname, uid_t uid),
34 void (*cleanup)(void *));
35 int
37 archive_write_header(struct archive *, struct archive_entry *);
38 ssize_t
40 archive_write_data(struct archive *, const void *, size_t);
41 int
43 archive_write_finish_entry(struct archive *);
44 int
46 archive_write_close(struct archive *);
47 int
49 archive_write_finish(struct archive *);
50
52 These functions provide a complete API for creating objects on disk from
53 struct archive_entry descriptions. They are most naturally used when
54 extracting objects from an archive using the archive_read() interface.
55 The general process is to read struct archive_entry objects from an ar‐
56 chive, then write those objects to a struct archive object created using
57 the archive_write_disk() family functions. This interface is deliber‐
58 ately very similar to the archive_write() interface used to write objects
59 to a streaming archive.
60 archive_write_disk_new()
62 Allocates and initializes a struct archive object suitable for
63 writing objects to disk.
64 archive_write_disk_set_skip_file()
66 Records the device and inode numbers of a file that should not be
67 overwritten. This is typically used to ensure that an extraction
68 process does not overwrite the archive from which objects are
69 being read. This capability is technically unnecessary but can
70 be a significant performance optimization in practice.
71 archive_write_disk_set_options()
73 The options field consists of a bitwise OR of one or more of the
74 following values:
75 ARCHIVE_EXTRACT_OWNER
76 The user and group IDs should be set on the restored
77 file. By default, the user and group IDs are not
78 restored.
79 ARCHIVE_EXTRACT_PERM
80 Full permissions (including SGID, SUID, and sticky bits)
81 should be restored exactly as specified, without obeying
82 the current umask. Note that SUID and SGID bits can only
83 be restored if the user and group ID of the object on
84 disk are correct. If ARCHIVE_EXTRACT_OWNER is not speci‐
85 fied, then SUID and SGID bits will only be restored if
86 the default user and group IDs of newly-created objects
87 on disk happen to match those specified in the archive
88 entry. By default, only basic permissions are restored,
89 and umask is obeyed.
90 ARCHIVE_EXTRACT_TIME
91 The timestamps (mtime, ctime, and atime) should be
92 restored. By default, they are ignored. Note that
93 restoring of atime is not currently supported.
94 ARCHIVE_EXTRACT_NO_OVERWRITE
95 Existing files on disk will not be overwritten. By
96 default, existing regular files are truncated and over‐
97 written; existing directories will have their permissions
98 updated; other pre-existing objects are unlinked and
99 recreated from scratch.
100 ARCHIVE_EXTRACT_UNLINK
101 Existing files on disk will be unlinked before any
102 attempt to create them. In some cases, this can prove to
103 be a significant performance improvement. By default,
104 existing files are truncated and rewritten, but the file
105 is not recreated. In particular, the default behavior
106 does not break existing hard links.
107 ARCHIVE_EXTRACT_ACL
108 Attempt to restore ACLs. By default, extended ACLs are
109 ignored.
110 ARCHIVE_EXTRACT_FFLAGS
111 Attempt to restore extended file flags. By default, file
112 flags are ignored.
113 ARCHIVE_EXTRACT_XATTR
114 Attempt to restore POSIX.1e extended attributes. By
115 default, they are ignored.
116 ARCHIVE_EXTRACT_SECURE_SYMLINKS
117 Refuse to extract any object whose final location would
118 be altered by a symlink on disk. This is intended to
119 help guard against a variety of mischief caused by ar‐
120 chives that (deliberately or otherwise) extract files
121 outside of the current directory. The default is not to
122 perform this check. If ARCHIVE_EXTRACT_UNLINK is speci‐
123 fied together with this option, the library will remove
124 any intermediate symlinks it finds and return an error
125 only if such symlink could not be removed.
126 ARCHIVE_EXTRACT_SECURE_NODOTDOT
127 Refuse to extract a path that contains a .. element any‐
128 where within it. The default is to not refuse such
129 paths. Note that paths ending in .. always cause an
130 error, regardless of this flag.
131 ARCHIVE_EXTRACT_SPARSE
132 Scan data for blocks of NUL bytes and try to recreate
133 them with holes. This results in sparse files, indepen‐
134 dent of whether the archive format supports or uses them.
135 archive_write_disk_set_group_lookup(),
137 archive_write_disk_set_user_lookup()
138 The struct archive_entry objects contain both names and ids that
139 can be used to identify users and groups. These names and ids
140 describe the ownership of the file itself and also appear in ACL
141 lists. By default, the library uses the ids and ignores the
142 names, but this can be overridden by registering user and group
143 lookup functions. To register, you must provide a lookup func‐
144 tion which accepts both a name and id and returns a suitable id.
145 You may also provide a void * pointer to a private data structure
146 and a cleanup function for that data. The cleanup function will
147 be invoked when the struct archive object is destroyed.
148 archive_write_disk_set_standard_lookup()
150 This convenience function installs a standard set of user and
151 group lookup functions. These functions use getpwnam(3) and
152 getgrnam(3) to convert names to ids, defaulting to the ids if the
153 names cannot be looked up. These functions also implement a sim‐
154 ple memory cache to reduce the number of calls to getpwnam(3) and
155 getgrnam(3).
156 archive_write_header()
158 Build and write a header using the data in the provided struct
159 archive_entry structure. See archive_entry(3) for information on
160 creating and populating struct archive_entry objects.
161 archive_write_data()
163 Write data corresponding to the header just written. Returns
164 number of bytes written or -1 on error.
165 archive_write_finish_entry()
167 Close out the entry just written. Ordinarily, clients never need
168 to call this, as it is called automatically by
169 archive_write_next_header() and archive_write_close() as needed.
170 archive_write_close()
172 Set any attributes that could not be set during the initial
173 restore. For example, directory timestamps are not restored ini‐
174 tially because restoring a subsequent file would alter that time‐
175 stamp. Similarly, non-writable directories are initially created
176 with write permissions (so that their contents can be restored).
177 The archive_write_disk_new library maintains a list of all such
178 deferred attributes and sets them when this function is invoked.
179 archive_write_finish()
181 Invokes archive_write_close() if it was not invoked manually,
182 then releases all resources.
183 More information about the struct archive object and the overall design
184 of the library can be found in the libarchive(3) overview. Many of these
185 functions are also documented under archive_write(3).
186
188 Most functions return ARCHIVE_OK (zero) on success, or one of several
189 non-zero error codes for errors. Specific error codes include:
190 ARCHIVE_RETRY for operations that might succeed if retried, ARCHIVE_WARN
191 for unusual conditions that do not prevent further operations, and
192 ARCHIVE_FATAL for serious errors that make remaining operations impossi‐
193 ble. The archive_errno() and archive_error_string() functions can be
194 used to retrieve an appropriate error code and a textual error message.
195 archive_write_disk_new() returns a pointer to a newly-allocated struct
197 archive object.
198 archive_write_data() returns a count of the number of bytes actually
200 written. On error, -1 is returned and the archive_errno() and
201 archive_error_string() functions will return appropriate values.
202
204 archive_read(3), archive_write(3), tar(1), libarchive(3)
205
207 The libarchive library first appeared in FreeBSD 5.3. The
208 archive_write_disk interface was added to libarchive 2.0 and first
209 appeared in FreeBSD 6.3.
210
212 The libarchive library was written by Tim Kientzle <kientzle@acm.org>.
213
215 Directories are actually extracted in two distinct phases. Directories
216 are created during archive_write_header(), but final permissions are not
217 set until archive_write_close(). This separation is necessary to cor‐
218 rectly handle borderline cases such as a non-writable directory contain‐
219 ing files, but can cause unexpected results. In particular, directory
220 permissions are not fully restored until the archive is closed. If you
221 use chdir(2) to change the current directory between calls to
222 archive_read_extract() or before calling archive_read_close(), you may
223 confuse the permission-setting logic with the result that directory per‐
224 missions are restored incorrectly.
225 The library attempts to create objects with filenames longer than
227 PATH_MAX by creating prefixes of the full path and changing the current
228 directory. Currently, this logic is limited in scope; the fixup pass
229 does not work correctly for such objects and the symlink security check
230 option disables the support for very long pathnames.
231 Restoring the path aa/../bb does create each intermediate directory. In
233 particular, the directory aa is created as well as the final object bb.
234 In theory, this can be exploited to create an entire directory heirarchy
235 with a single request. Of course, this does not work if the
236 ARCHIVE_EXTRACT_NODOTDOT option is specified.
237 Implicit directories are always created obeying the current umask.
239 Explicit objects are created obeying the current umask unless
240 ARCHIVE_EXTRACT_PERM is specified, in which case they current umask is
241 ignored.
242 SGID and SUID bits are restored only if the correct user and group could
244 be set. If ARCHIVE_EXTRACT_OWNER is not specified, then no attempt is
245 made to set the ownership. In this case, SGID and SUID bits are restored
246 only if the user and group of the final object happen to match those
247 specified in the entry.
248 The “standard” user-id and group-id lookup functions are not the defaults
250 because getgrnam(3) and getpwnam(3) are sometimes too large for particu‐
251 lar applications. The current design allows the application author to
252 use a more compact implementation when appropriate.
253 There should be a corresponding archive_read_disk interface that walks a
255 directory heirarchy and returns archive entry objects.
256BSD August 5, 2008 BSD