NEWCHAN(9) NEWCHAN(9)
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 struc-
ture:
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 other-
wise.
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NEWCHAN(9) NEWCHAN(9)
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 pro-
cess). 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 incre-
mented. 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 suit-
able for open(2); if Acreate, perm should be valid file per-
missions. 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
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NEWCHAN(9) NEWCHAN(9)
DIAGNOSTICS
Most functions call error(9) on any sort of error.
SEE ALSO
ref(9)
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