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_SECURE_NOABSOLUTEPATHS
99 Refuse to extract an absolute path. The default is to
100 not refuse such paths.
101 ARCHIVE_EXTRACT_SECURE_NODOTDOT
102 Refuse to extract a path that contains a .. element any‐
103 where within it. The default is to not refuse such
104 paths. Note that paths ending in .. always cause an
105 error, regardless of this flag.
106 ARCHIVE_EXTRACT_SECURE_SYMLINKS
107 Refuse to extract any object whose final location would
108 be altered by a symlink on disk. This is intended to
109 help guard against a variety of mischief caused by ar‐
110 chives that (deliberately or otherwise) extract files
111 outside of the current directory. The default is not to
112 perform this check. If
113 ARCHIVE_EXTRACT_SPARSE
114 Scan data for blocks of NUL bytes and try to recreate
115 them with holes. This results in sparse files, indepen‐
116 dent of whether the archive format supports or uses them.
117 ARCHIVE_EXTRACT_UNLINK is specified together with this
118 option, the library will remove any intermediate symlinks
119 it finds and return an error only if such symlink could
120 not be removed.
121 ARCHIVE_EXTRACT_TIME
122 The timestamps (mtime, ctime, and atime) should be
123 restored. By default, they are ignored. Note that
124 restoring of atime is not currently supported.
125 ARCHIVE_EXTRACT_UNLINK
126 Existing files on disk will be unlinked before any
127 attempt to create them. In some cases, this can prove to
128 be a significant performance improvement. By default,
129 existing files are truncated and rewritten, but the file
130 is not recreated. In particular, the default behavior
131 does not break existing hard links.
132 ARCHIVE_EXTRACT_XATTR
133 Attempt to restore extended file attributes. By default,
134 they are ignored. See xattr(7) (Linux), xattr(2) (Mac OS
135 X), or getextattr(8) (FreeBSD) for more information on
136 extended file attributes.
137 archive_write_disk_set_group_lookup(),
139 archive_write_disk_set_user_lookup()
140 The struct archive_entry objects contain both names and ids that
141 can be used to identify users and groups. These names and ids
142 describe the ownership of the file itself and also appear in ACL
143 lists. By default, the library uses the ids and ignores the
144 names, but this can be overridden by registering user and group
145 lookup functions. To register, you must provide a lookup func‐
146 tion which accepts both a name and id and returns a suitable id.
147 You may also provide a void * pointer to a private data structure
148 and a cleanup function for that data. The cleanup function will
149 be invoked when the struct archive object is destroyed.
150 archive_write_disk_set_standard_lookup()
152 This convenience function installs a standard set of user and
153 group lookup functions. These functions use getpwnam(3) and
154 getgrnam(3) to convert names to ids, defaulting to the ids if the
155 names cannot be looked up. These functions also implement a sim‐
156 ple memory cache to reduce the number of calls to getpwnam(3) and
157 getgrnam(3).
158 More information about the struct archive object and the overall design
159 of the library can be found in the libarchive(3) overview. Many of these
160 functions are also documented under archive_write(3).
161
163 Most functions return ARCHIVE_OK (zero) on success, or one of several
164 non-zero error codes for errors. Specific error codes include:
165 ARCHIVE_RETRY for operations that might succeed if retried, ARCHIVE_WARN
166 for unusual conditions that do not prevent further operations, and
167 ARCHIVE_FATAL for serious errors that make remaining operations impossi‐
168 ble.
169 archive_write_disk_new() returns a pointer to a newly-allocated struct
171 archive object.
172 archive_write_data() returns a count of the number of bytes actually
174 written, or -1 on error.
175
177 Detailed error codes and textual descriptions are available from the
178 archive_errno() and archive_error_string() functions.
179
181 archive_read(3), archive_write(3), tar(1), libarchive(3)
182
184 The libarchive library first appeared in FreeBSD 5.3. The
185 archive_write_disk interface was added to libarchive 2.0 and first
186 appeared in FreeBSD 6.3.
187
189 The libarchive library was written by Tim Kientzle <kientzle@acm.org>.
190
192 Directories are actually extracted in two distinct phases. Directories
193 are created during archive_write_header(), but final permissions are not
194 set until archive_write_close(). This separation is necessary to cor‐
195 rectly handle borderline cases such as a non-writable directory contain‐
196 ing files, but can cause unexpected results. In particular, directory
197 permissions are not fully restored until the archive is closed. If you
198 use chdir(2) to change the current directory between calls to
199 archive_read_extract() or before calling archive_read_close(), you may
200 confuse the permission-setting logic with the result that directory per‐
201 missions are restored incorrectly.
202 The library attempts to create objects with filenames longer than
204 PATH_MAX by creating prefixes of the full path and changing the current
205 directory. Currently, this logic is limited in scope; the fixup pass
206 does not work correctly for such objects and the symlink security check
207 option disables the support for very long pathnames.
208 Restoring the path aa/../bb does create each intermediate directory. In
210 particular, the directory aa is created as well as the final object bb.
211 In theory, this can be exploited to create an entire directory hierarchy
212 with a single request. Of course, this does not work if the
213 ARCHIVE_EXTRACT_NODOTDOT option is specified.
214 Implicit directories are always created obeying the current umask.
216 Explicit objects are created obeying the current umask unless
217 ARCHIVE_EXTRACT_PERM is specified, in which case they current umask is
218 ignored.
219 SGID and SUID bits are restored only if the correct user and group could
221 be set. If ARCHIVE_EXTRACT_OWNER is not specified, then no attempt is
222 made to set the ownership. In this case, SGID and SUID bits are restored
223 only if the user and group of the final object happen to match those
224 specified in the entry.
225 The “standard” user-id and group-id lookup functions are not the defaults
227 because getgrnam(3) and getpwnam(3) are sometimes too large for particu‐
228 lar applications. The current design allows the application author to
229 use a more compact implementation when appropriate.
230 There should be a corresponding archive_read_disk interface that walks a
232 directory hierarchy and returns archive entry objects.
233BSD April 3, 2017 BSD