[manual index][section index]


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:

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:

Access file for information, as in the stat command or call.
Access file as directory (the QTDIR bit of its qid.type must be set).
Access for I/O.
Access directory to be mounted upon.
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.





NEWCHAN(10.2 ) Rev:  Tue Mar 31 02:42:39 GMT 2015