newchan, chanfree, cclose, eqqid, eqchan, isdir, fdtochan, namec - channel operations 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)

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

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 .

Most functions call error (10.2) on any sort of error. /os/port/chan.c

/emu/port/chan.c

ref (10.2)