Contents of /tags/mkinitrd-6_3_4/busybox/docs/tar_pax.txt
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Thu Dec 16 01:27:43 2010 UTC (13 years, 9 months ago) by niro
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Thu Dec 16 01:27:43 2010 UTC (13 years, 9 months ago) by niro
File MIME type: text/plain
File size: 11784 byte(s)
tagged 'mkinitrd-6_3_4'
1 | 'pax headers' is POSIX 2003 (iirc) addition designed to fix |
2 | tar format limitations - older tar format has fixed fields |
3 | for everything (filename, uid, filesize etc) which can overflow. |
4 | |
5 | pax Header Block |
6 | |
7 | The pax header block shall be identical to the ustar header block |
8 | described in ustar Interchange Format, except that two additional |
9 | typeflag values are defined: |
10 | |
11 | x |
12 | Represents extended header records for the following file in |
13 | the archive (which shall have its own ustar header block). |
14 | |
15 | g |
16 | Represents global extended header records for the following |
17 | files in the archive. Each value shall affect all subsequent files |
18 | that do not override that value in their own extended header |
19 | record and until another global extended header record is reached |
20 | that provides another value for the same field. The typeflag g |
21 | global headers should not be used with interchange media that |
22 | could suffer partial data loss in transporting the archive. |
23 | |
24 | For both of these types, the size field shall be the size of the |
25 | extended header records in octets. The other fields in the header |
26 | block are not meaningful to this version of the pax utility. |
27 | However, if this archive is read by a pax utility conforming to |
28 | the ISO POSIX-2:1993 standard, the header block fields are used to |
29 | create a regular file that contains the extended header records as |
30 | data. Therefore, header block field values should be selected to |
31 | provide reasonable file access to this regular file. |
32 | |
33 | A further difference from the ustar header block is that data |
34 | blocks for files of typeflag 1 (the digit one) (hard link) may be |
35 | included, which means that the size field may be greater than |
36 | zero. |
37 | |
38 | pax Extended Header |
39 | |
40 | An extended header shall consist of one or more records, each |
41 | constructed as follows: |
42 | |
43 | "%d %s=%s\n", <length>, <keyword>, <value> |
44 | |
45 | The <length> field shall be the decimal length of the extended |
46 | header record in octets, including length string itself and the |
47 | trailing <newline>. |
48 | |
49 | [skip] |
50 | |
51 | atime |
52 | The file access time for the following file(s), equivalent to |
53 | the value of the st_atime member of the stat structure for a file, |
54 | as described by the stat() function. The access time shall be |
55 | restored if the process has the appropriate privilege required to |
56 | do so. The format of the <value> shall be as described in pax |
57 | Extended Header File Times. |
58 | |
59 | charset |
60 | The name of the character set used to encode the data in the |
61 | following file(s). |
62 | |
63 | The encoding is included in an extended header for information |
64 | only; when pax is used as described in IEEE Std 1003.1-2001, it |
65 | shall not translate the file data into any other encoding. The |
66 | BINARY entry indicates unencoded binary data. |
67 | |
68 | When used in write or copy mode, it is implementation-defined |
69 | whether pax includes a charset extended header record for a file. |
70 | |
71 | comment |
72 | A series of characters used as a comment. All characters in |
73 | the <value> field shall be ignored by pax. |
74 | |
75 | gid |
76 | The group ID of the group that owns the file, expressed as a |
77 | decimal number using digits from the ISO/IEC 646:1991 standard. |
78 | This record shall override the gid field in the following header |
79 | block(s). When used in write or copy mode, pax shall include a gid |
80 | extended header record for each file whose group ID is greater |
81 | than 2097151 (octal 7777777). |
82 | |
83 | gname |
84 | The group of the file(s), formatted as a group name in the |
85 | group database. This record shall override the gid and gname |
86 | fields in the following header block(s), and any gid extended |
87 | header record. When used in read, copy, or list mode, pax shall |
88 | translate the name from the UTF-8 encoding in the header record to |
89 | the character set appropriate for the group database on the |
90 | receiving system. If any of the UTF-8 characters cannot be |
91 | translated, and if the -o invalid= UTF-8 option is not specified, |
92 | the results are implementation-defined. When used in write or copy |
93 | mode, pax shall include a gname extended header record for each |
94 | file whose group name cannot be represented entirely with the |
95 | letters and digits of the portable character set. |
96 | |
97 | linkpath |
98 | The pathname of a link being created to another file, of any |
99 | type, previously archived. This record shall override the linkname |
100 | field in the following ustar header block(s). The following ustar |
101 | header block shall determine the type of link created. If typeflag |
102 | of the following header block is 1, it shall be a hard link. If |
103 | typeflag is 2, it shall be a symbolic link and the linkpath value |
104 | shall be the contents of the symbolic link. The pax utility shall |
105 | translate the name of the link (contents of the symbolic link) |
106 | from the UTF-8 encoding to the character set appropriate for the |
107 | local file system. When used in write or copy mode, pax shall |
108 | include a linkpath extended header record for each link whose |
109 | pathname cannot be represented entirely with the members of the |
110 | portable character set other than NUL. |
111 | |
112 | mtime |
113 | The file modification time of the following file(s), |
114 | equivalent to the value of the st_mtime member of the stat |
115 | structure for a file, as described in the stat() function. This |
116 | record shall override the mtime field in the following header |
117 | block(s). The modification time shall be restored if the process |
118 | has the appropriate privilege required to do so. The format of the |
119 | <value> shall be as described in pax Extended Header File Times. |
120 | |
121 | path |
122 | The pathname of the following file(s). This record shall |
123 | override the name and prefix fields in the following header |
124 | block(s). The pax utility shall translate the pathname of the file |
125 | from the UTF-8 encoding to the character set appropriate for the |
126 | local file system. |
127 | |
128 | When used in write or copy mode, pax shall include a path |
129 | extended header record for each file whose pathname cannot be |
130 | represented entirely with the members of the portable character |
131 | set other than NUL. |
132 | |
133 | realtime.any |
134 | The keywords prefixed by "realtime." are reserved for future |
135 | standardization. |
136 | |
137 | security.any |
138 | The keywords prefixed by "security." are reserved for future |
139 | standardization. |
140 | |
141 | size |
142 | The size of the file in octets, expressed as a decimal number |
143 | using digits from the ISO/IEC 646:1991 standard. This record shall |
144 | override the size field in the following header block(s). When |
145 | used in write or copy mode, pax shall include a size extended |
146 | header record for each file with a size value greater than |
147 | 8589934591 (octal 77777777777). |
148 | |
149 | uid |
150 | The user ID of the file owner, expressed as a decimal number |
151 | using digits from the ISO/IEC 646:1991 standard. This record shall |
152 | override the uid field in the following header block(s). When used |
153 | in write or copy mode, pax shall include a uid extended header |
154 | record for each file whose owner ID is greater than 2097151 (octal |
155 | 7777777). |
156 | |
157 | uname |
158 | The owner of the following file(s), formatted as a user name |
159 | in the user database. This record shall override the uid and uname |
160 | fields in the following header block(s), and any uid extended |
161 | header record. When used in read, copy, or list mode, pax shall |
162 | translate the name from the UTF-8 encoding in the header record to |
163 | the character set appropriate for the user database on the |
164 | receiving system. If any of the UTF-8 characters cannot be |
165 | translated, and if the -o invalid= UTF-8 option is not specified, |
166 | the results are implementation-defined. When used in write or copy |
167 | mode, pax shall include a uname extended header record for each |
168 | file whose user name cannot be represented entirely with the |
169 | letters and digits of the portable character set. |
170 | |
171 | If the <value> field is zero length, it shall delete any header |
172 | block field, previously entered extended header value, or global |
173 | extended header value of the same name. |
174 | |
175 | If a keyword in an extended header record (or in a -o |
176 | option-argument) overrides or deletes a corresponding field in the |
177 | ustar header block, pax shall ignore the contents of that header |
178 | block field. |
179 | |
180 | Unlike the ustar header block fields, NULs shall not delimit |
181 | <value>s; all characters within the <value> field shall be |
182 | considered data for the field. None of the length limitations of |
183 | the ustar header block fields in ustar Header Block shall apply to |
184 | the extended header records. |
185 | |
186 | pax Extended Header File Times |
187 | |
188 | Time records shall be formatted as a decimal representation of the |
189 | time in seconds since the Epoch. If a period ( '.' ) decimal point |
190 | character is present, the digits to the right of the point shall |
191 | represent the units of a subsecond timing granularity. In read or |
192 | copy mode, the pax utility shall truncate the time of a file to |
193 | the greatest value that is not greater than the input header |
194 | file time. In write or copy mode, the pax utility shall output a |
195 | time exactly if it can be represented exactly as a decimal number, |
196 | and otherwise shall generate only enough digits so that the same |
197 | time shall be recovered if the file is extracted on a system whose |
198 | underlying implementation supports the same time granularity. |
199 | |
200 | Example from Linux kernel archive tarball: |
201 | |
202 | 00000000 70 61 78 5f 67 6c 6f 62 61 6c 5f 68 65 61 64 65 |pax_global_heade| |
203 | 00000010 72 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |r...............| |
204 | 00000020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
205 | 00000030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
206 | 00000040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
207 | 00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
208 | 00000060 00 00 00 00 30 30 30 30 36 36 36 00 30 30 30 30 |....0000666.0000| |
209 | 00000070 30 30 30 00 30 30 30 30 30 30 30 00 30 30 30 30 |000.0000000.0000| |
210 | 00000080 30 30 30 30 30 36 34 00 30 30 30 30 30 30 30 30 |0000064.00000000| |
211 | 00000090 30 30 30 00 30 30 31 34 30 35 33 00 67 00 00 00 |000.0014053.g...| |
212 | 000000a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
213 | 000000b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
214 | 000000c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
215 | 000000d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
216 | 000000e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
217 | 000000f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
218 | 00000100 00 75 73 74 61 72 00 30 30 67 69 74 00 00 00 00 |.ustar.00git....| |
219 | 00000110 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
220 | 00000120 00 00 00 00 00 00 00 00 00 67 69 74 00 00 00 00 |.........git....| |
221 | 00000130 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
222 | 00000140 00 00 00 00 00 00 00 00 00 30 30 30 30 30 30 30 |.........0000000| |
223 | 00000150 00 30 30 30 30 30 30 30 00 00 00 00 00 00 00 00 |.0000000........| |
224 | 00000160 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
225 | 00000170 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
226 | 00000180 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
227 | 00000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
228 | 000001a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
229 | 000001b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
230 | 000001c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
231 | 000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
232 | 000001e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
233 | 000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
234 | 00000200 35 32 20 63 6f 6d 6d 65 6e 74 3d 62 31 30 35 30 |52 comment=b1050| |
235 | 00000210 32 62 32 32 61 31 32 30 39 64 36 62 34 37 36 33 |2b22a1209d6b4763| |
236 | 00000220 39 64 38 38 62 38 31 32 62 32 31 66 62 35 39 34 |9d88b812b21fb594| |
237 | 00000230 39 65 34 0a 00 00 00 00 00 00 00 00 00 00 00 00 |9e4.............| |
238 | 00000240 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| |
239 | ... |