NEWCHAN(10.2)
NAME
newchan, chanfree, cclose, eqqid, eqchan, isdir, fdtochan, namec − channel operations
SYNOPSIS
Chan*newchan(void)
voidchanfree(Chan *c)
inteqqid(Qid a, Qid b)
inteqchan(Chan *a, Chan *b, int pathonly)
voidisdir(Chan *c)
Chan*fdtochan(Fgrp *f, int fd, int mode, int chkmnt, int iref)
Chan*namec(char *pathname, int amode, int omode, ulong perm)
voidcclose(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) */ Cname* name; /* 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(10.2).
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(10.2), 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->env->fgrp, the file descriptor group for the current process). If mode is a valid mode for sys-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(10.2) 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 sys-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.
DIAGNOSTICS
Most functions call error(10.2) on any sort of error.
SOURCE
/os/port/chan.c
/emu/port/chan.c