1ARCHIVE_WRITE_DISK(3)    BSD Library Functions Manual    ARCHIVE_WRITE_DISK(3)
2

NAME

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

LIBRARY

11     Streaming Archive Library (libarchive, -larchive)
12

SYNOPSIS

14     #include <archive.h>
15
16     struct archive *
17     archive_write_disk_new(void);
18
19     int
20     archive_write_disk_set_options(struct archive *, int flags);
21
22     int
23     archive_write_disk_set_skip_file(struct archive *, dev_t, ino_t);
24
25     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
30     int
31     archive_write_disk_set_standard_lookup(struct archive *);
32
33     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

DESCRIPTION

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
48     archive_write_disk_new()
49             Allocates and initializes a struct archive object suitable for
50             writing objects to disk.
51
52     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
59     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
143     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
156     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

RETURN VALUES

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
175     archive_write_disk_new() returns a pointer to a newly-allocated struct
176     archive object.
177
178     archive_write_data() returns a count of the number of bytes actually
179     written, or -1 on error.
180

ERRORS

182     Detailed error codes and textual descriptions are available from the
183     archive_errno() and archive_error_string() functions.
184

SEE ALSO

186     tar(1), archive_read(3), archive_write(3), libarchive(3)
187

HISTORY

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

AUTHORS

194     The libarchive library was written by Tim Kientzle <kientzle@acm.org>.
195

BUGS

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
208     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
214     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
220     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
225     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
231     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
236     There should be a corresponding archive_read_disk interface that walks a
237     directory hierarchy and returns archive entry objects.
238
239BSD                            January 19, 2020                            BSD
Impressum