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bind 4.6 KB

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  1. .TH BIND 2
  2. .SH NAME
  3. bind, mount, unmount \- change name space
  4. .SH SYNOPSIS
  5. .B #include <u.h>
  6. .br
  7. .B #include <libc.h>
  8. .PP
  9. .B
  10. int bind(char *name, char *old, int flag)
  11. .PP
  12. .B
  13. int mount(int fd, int afd, char *old, int flag, char *aname)
  14. .PP
  15. .B
  16. int unmount(char *name, char *old)
  17. .SH DESCRIPTION
  18. .I Bind
  19. and
  20. .I mount
  21. modify the file name space of the current process and other
  22. processes in its name space group
  23. (see
  24. .IR fork (2)).
  25. For both calls,
  26. .I old
  27. is the name of an existing file or directory in the
  28. current name space where the modification is to be made.
  29. The name
  30. .I old
  31. is
  32. .I evaluated
  33. as described in
  34. .IR intro (2),
  35. except that no translation of the final path element is done.
  36. .PP
  37. For
  38. .IR bind ,
  39. .I name
  40. is the name of another (or possibly the same)
  41. existing file or directory in
  42. the current name space.
  43. After a successful
  44. .I bind
  45. call, the file name
  46. .I old
  47. is an alias for the object originally named by
  48. .IR name ;
  49. if the modification doesn't hide it,
  50. .I name
  51. will also still refer to its original file.
  52. The evaluation of
  53. .I new
  54. happens at the time of the
  55. .IR bind ,
  56. not when the binding is later used.
  57. .PP
  58. The
  59. .I fd
  60. argument to
  61. .I mount
  62. is a file descriptor of an open network connection
  63. or pipe to a file server, while
  64. .I afd
  65. is a authentication file descriptor as created by
  66. .IR fauth (2)
  67. and subsequently authenticated.
  68. If authentication is not required,
  69. .I afd
  70. should be -1.
  71. The
  72. .I old
  73. file must be a directory.
  74. After a successful
  75. .I mount
  76. the file tree
  77. .I served
  78. (see below) by
  79. .I fd
  80. will be visible with its root directory having name
  81. .IR old .
  82. .PP
  83. The
  84. .I flag
  85. controls details of the modification made to the name space.
  86. In the following,
  87. .I new
  88. refers to the file
  89. as defined by
  90. .I name
  91. or the root directory served by
  92. .IR fd .
  93. Either both
  94. .I old
  95. and new files must be directories,
  96. or both must not be directories.
  97. .I Flag
  98. can be one of:
  99. .TF MBEFORE
  100. .TP
  101. .B MREPL
  102. Replace the
  103. .I old
  104. file by the new one.
  105. Henceforth, an evaluation of
  106. .I old
  107. will be translated to the new file.
  108. If they are directories (for
  109. .IR mount ,
  110. this condition is true by definition),
  111. .I old
  112. becomes a
  113. .I "union directory"
  114. consisting of one directory (the new file).
  115. .TP
  116. .B MBEFORE
  117. Both the
  118. .I old
  119. and new files must be directories.
  120. Add the constituent files of the new directory
  121. to the union directory at
  122. .I old
  123. so its contents appear first in the union.
  124. After an
  125. .B MBEFORE
  126. .I bind
  127. or
  128. .IR mount ,
  129. the new directory will be searched first when evaluating file names
  130. in the union directory.
  131. .TP
  132. .B MAFTER
  133. Like
  134. .B MBEFORE
  135. but the new directory goes at the end of the union.
  136. .PD
  137. .PP
  138. The flags are defined in
  139. .BR <libc.h> .
  140. In addition, there is an
  141. .B MCREATE
  142. flag that can be OR'd with any of the above.
  143. When a
  144. .I create
  145. system call (see
  146. .IR open (2))
  147. attempts to create in a union directory, and the file does not exist,
  148. the elements of the union are searched in order until one is found
  149. with
  150. .B MCREATE
  151. set.
  152. The file is created in that directory; if that attempt fails,
  153. the
  154. .I create
  155. fails.
  156. .PP
  157. Finally, the
  158. .B MCACHE
  159. flag, valid for
  160. .I mount
  161. only, turns on caching for files made available by the mount.
  162. By default, file contents are always retrieved from the server.
  163. With caching enabled, the kernel may instead use a local cache to satisfy
  164. .IR read (5)
  165. requests for files accessible through this mount point.
  166. The currency of cached data for a file is verified at each
  167. .IR open (5)
  168. of the file from this client machine.
  169. .PP
  170. With
  171. .IR mount ,
  172. the file descriptor
  173. .I fd
  174. must be open for reading and writing
  175. and prepared to respond to 9P messages
  176. (see Section 5).
  177. After the
  178. .IR mount ,
  179. the file tree starting at
  180. .I old
  181. is served by a kernel
  182. .IR mnt (3)
  183. device.
  184. That device will turn operations in the tree into messages on
  185. .IR fd .
  186. .I Aname
  187. selects among different
  188. file trees on the server; the null string chooses the default tree.
  189. .PP
  190. The file descriptor
  191. .I fd
  192. is automatically closed by a successful
  193. .I mount
  194. call.
  195. .PP
  196. The effects of
  197. .I bind
  198. and
  199. .I mount
  200. can be undone by
  201. .IR unmount .
  202. If
  203. .I name
  204. is zero, everything bound to or mounted upon
  205. .I old
  206. is unbound or unmounted.
  207. If
  208. .I name
  209. is not zero, it is evaluated as described above for
  210. .IR bind ,
  211. and the effect of binding or mounting that particular result on
  212. .I old
  213. is undone.
  214. .SH SOURCE
  215. .B /sys/src/libc/9syscall
  216. .SH SEE ALSO
  217. .IR bind (1),
  218. .IR intro (2),
  219. .IR fcall (2),
  220. .IR auth (2)
  221. (particularly
  222. .BR amount ),
  223. .IR intro (5),
  224. .IR mnt (3),
  225. .IR srv (3)
  226. .SH DIAGNOSTICS
  227. The return value is a positive integer (a unique sequence number) for
  228. success, -1 for failure.
  229. These routines set
  230. .IR errstr .
  231. .SH BUGS
  232. .I Mount
  233. will not return until it has successfully attached
  234. to the file server, so the process doing a
  235. .I mount
  236. cannot be the one serving.