1ARCHIVE_WRITE_DISK(3) BSD Library Functions Manual ARCHIVE_WRITE_DISK(3) 2 3NAME 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 10LIBRARY 11 Streaming Archive Library (libarchive, -larchive) 12 13SYNOPSIS 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 38DESCRIPTION 39 These functions provide a complete API for creating objects on disk from 40 struct archive_entry descriptions. They are most naturally used when ex‐ 41 tracting objects from an archive using the archive_read() interface. The 42 general process is to read struct archive_entry objects from an archive, 43 then write those objects to a struct archive object created using the 44 archive_write_disk() family functions. This interface is deliberately 45 very similar to the archive_write() interface used to write objects to a 46 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 be‐ 56 ing read. This capability is technically unnecessary but can be 57 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, ex‐ 64 tended 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 de‐ 71 fault, 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 de‐ 79 fault, existing regular files are truncated and overwrit‐ 80 ten; existing directories will have their permissions up‐ 81 dated; other pre-existing objects are unlinked and recre‐ 82 ated 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 re‐ 86 stored. 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 er‐ 110 ror, 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 re‐ 128 stored. By default, they are ignored. Note that restor‐ 129 ing of atime is not currently supported. 130 ARCHIVE_EXTRACT_UNLINK 131 Existing files on disk will be unlinked before any at‐ 132 tempt 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 167RETURN 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 181ERRORS 182 Detailed error codes and textual descriptions are available from the 183 archive_errno() and archive_error_string() functions. 184 185SEE ALSO 186 tar(1), archive_read(3), archive_write(3), libarchive(3) 187 188HISTORY 189 The libarchive library first appeared in FreeBSD 5.3. The 190 archive_write_disk interface was added to libarchive 2.0 and first ap‐ 191 peared in FreeBSD 6.3. 192 193AUTHORS 194 The libarchive library was written by Tim Kientzle <kientzle@acm.org>. 195 196BUGS 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. Ex‐ 221 plicit 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 240