ref: 370bfd26ce5ffd9a06a314a20d1691cc6b15b712
dir: /sys/man/2/bind/
.TH BIND 2 .SH NAME bind, mount, unmount \- change name space .SH SYNOPSIS .B #include <u.h> .br .B #include <libc.h> .PP .B int bind(char *name, char *old, int flag) .PP .B int mount(int fd, int afd, char *old, int flag, char *aname) .PP .B int unmount(char *name, char *old) .SH DESCRIPTION .I Bind and .I mount modify the file name space of the current process and other processes in its name space group (see .IR fork (2)). For both calls, .I old is the name of an existing file or directory in the current name space where the modification is to be made. The name .I old is .I evaluated as described in .IR intro (2), except that no translation of the final path element is done. .PP For .IR bind , .I name is the name of another (or possibly the same) existing file or directory in the current name space. After a successful .I bind call, the file name .I old is an alias for the object originally named by .IR name ; if the modification doesn't hide it, .I name will also still refer to its original file. The evaluation of .I new happens at the time of the .IR bind , not when the binding is later used. .PP The .I fd argument to .I mount is a file descriptor of an open network connection or pipe to a file server, while .I afd is a authentication file descriptor as created by .IR fauth (2) and subsequently authenticated. If authentication is not required, .I afd should be -1. The .I old file must be a directory. After a successful .I mount the file tree .I served (see below) by .I fd will be visible with its root directory having name .IR old . .PP The .I flag controls details of the modification made to the name space. In the following, .I new refers to the file as defined by .I name or the root directory served by .IR fd . Either both .I old and new files must be directories, or both must not be directories. .I Flag can be one of: .TF MBEFORE .TP .B MREPL Replace the .I old file by the new one. Henceforth, an evaluation of .I old will be translated to the new file. If they are directories (for .IR mount , this condition is true by definition), .I old becomes a .I "union directory" consisting of one directory (the new file). .TP .B MBEFORE Both the .I old and new files must be directories. Add the constituent files of the new directory to the union directory at .I old so its contents appear first in the union. After an .B MBEFORE .I bind or .IR mount , the new directory will be searched first when evaluating file names in the union directory. .TP .B MAFTER Like .B MBEFORE but the new directory goes at the end of the union. .PD .PP The flags are defined in .BR <libc.h> . In addition, there is an .B MCREATE flag that can be OR'd with any of the above. When a .I create system call (see .IR open (2)) attempts to create in a union directory, and the file does not exist, the elements of the union are searched in order until one is found with .B MCREATE set. The file is created in that directory; if that attempt fails, the .I create fails. .PP Finally, the .B MCACHE flag, valid for .I mount only, turns on caching for files made available by the mount. By default, file contents are always retrieved from the server. With caching enabled, the kernel may instead use a local cache to satisfy .IR read (5) requests for files accessible through this mount point. The currency of cached data for a file is verified at each .IR open (5) of the file from this client machine. .PP With .IR mount , the file descriptor .I fd must be open for reading and writing and prepared to respond to 9P messages (see Section 5). After the .IR mount , the file tree starting at .I old is served by a kernel .IR mnt (3) device. That device will turn operations in the tree into messages on .IR fd . .I Aname selects among different file trees on the server; the null string chooses the default tree. .PP The file descriptor .I fd is automatically closed by a successful .I mount call. .PP The effects of .I bind and .I mount can be undone by .IR unmount . If .I name is zero, everything bound to or mounted upon .I old is unbound or unmounted. If .I name is not zero, it is evaluated as described above for .IR bind , and the effect of binding or mounting that particular result on .I old is undone. .SH SOURCE .B /sys/src/libc/9syscall .SH SEE ALSO .IR bind (1), .IR intro (2), .IR fcall (2), .IR auth (2) (particularly .BR amount ), .IR intro (5), .IR mnt (3), .IR srv (3) .SH DIAGNOSTICS The return value is a positive integer (a unique sequence number) for success, -1 for failure. These routines set .IR errstr . .SH BUGS .I Mount will not return until it has successfully attached to the file server, so the process doing a .I mount cannot be the one serving.