Plan 9 /sys/man/9/newchan

NAME

newchan, chanfree, cclose, eqqid, eqchan, isdir, fdtochan, namec – channel operations

SYNOPSIS

Chan* newchan(void)
void    chanfree(Chan *c)
int     eqqid(Qid a, Qid b)
int     eqchan(Chan *a, Chan *b, int pathonly)
void    isdir(Chan *c)
Chan* fdtochan(Fgrp *f, int fd, int mode, int chkmnt, int iref)
Chan* namec(char *pathname, int amode, int omode, ulong perm)
void    cclose(Chan *c)

DESCRIPTION

A value of type Chan represents a kernel channel for I/O and name space operations. It has the following public structure:

typedef struct Chan{ ushort      type;         /* driver name */ ulong       dev;          /* instance number */ ushort      mode;         /* open mode */ ushort      flag;         /* COPEN set once opened */ ulong       offset;       /* current file offset */ Qid         qid;          /* unique id (path, vers) */ Path*       path;/* name by which it was accessed */

Newchan returns a pointer to a newly allocated channel (sleeping if necessary until memory is available). Device drivers do not normally call newchan directly, but instead allocate channels using either devattach, when a process attaches to the device's root, or devclone, when an existing channel is cloned; see devattach(9).
Chanfree frees the channel structure c for reuse.
Eqqid returns 1 if Qid values a and b are equal (ie, both their path and vers members are equal); it returns 0 otherwise.
Eqchan returns 1 if a and b have the same qid, type and dev members (ie, they represent the same file); it returns 0 otherwise. If pathonly is non–zero, the comparison of the two qid members compares only their path values, ignoring the version field vers.
Isdir checks that a given channel c is a directory. If so, it returns; otherwise, it generates an error(9), Enotdir.
The Fgrp structure represents an array of open files, each represented by a Chan, indexed by integer file descriptors. A given Fgrp can be shared between processes.
Fdtochan returns a pointer to the Chan corresponding to file descriptor fd in file descriptor group f (almost invariably up–>fgrp, the file descriptor group for the current process). If mode is a valid mode for open(2), typically OREAD, OWRITE or ORDWR, it must correspond to the mode with which fd was originally opened; if mode is –1, no check is made. If chkmnt is non–zero, c must not be a channel in use by the mount driver mnt(3). On successful return, if iref is non–zero, the channel's reference count has been incremented. Fdtochan calls error(9) if it detects invalid uses, in particular an invalid file descriptor fd.
Namec looks up a pathname in the current name space and returns a channel. Amode determines the mode of look up, and must be one of the constants below:
Aaccess   Access file for information, as in the stat command or call.
Atodir    Access file as directory (the QTDIR bit of its qid.type must be set).
Aopen     Access for I/O.
Amount    Access directory to be mounted upon.
Acreate   File is to be created.
If amode is Aopen or Acreate, omode should be a mode suitable for open(2); if Acreate, perm should be valid file permissions. In all other cases, omode and perm can be zero.
Cclose decrements the reference count on c; if no further references remain, it calls the corresponding device's Dev.close to close the channel, and frees c.

SOURCE

/sys/src/9/port/chan.c

DIAGNOSTICS

Most functions call error(9) on any sort of error.


	newchan, chanfree, cclose, eqqid, eqchan, isdir, fdtochan, namec – channel operations