DEVFS_CDEVPRIV(9)

NAME
devfs_set_cdevpriv, devfs_get_cdevpriv, devfs_clear_cdevpriv, devfs_foreach_cdevpriv - manage per-open filedescriptor data for devices

SYNOPSIS
#include <sys/param.h>
#include <sys/conf.h>

    typedef	void d_priv_dtor_t(void *data);

int
devfs_get_cdevpriv(void **datap);
int
devfs_set_cdevpriv(void *priv, d_priv_dtor_t *dtr);
void
devfs_clear_cdevpriv(void);
int
devfs_foreach_cdevpriv(struct cdev *dev, int (*cb)(void *data, void *arg), void *arg);

DESCRIPTION
The devfs_xxx_cdevpriv() family of functions allows the cdev driver methods to associate some driver-specific data with each user process open(2) of the device special file. Currently, functioning of these functions is restricted to the context of the cdevsw switch method calls performed as devfs(4) operations in response to system calls that use filedescriptors.

The devfs_set_cdevpriv() function associates a data pointed by priv with current calling context (filedescriptor). The data may be retrieved later, possibly from another call performed on this filedescriptor, by the devfs_get_cdevpriv() function. The devfs_clear_cdevpriv() disassociates previously attached data from context. Immediately after devfs_clear_cdevpriv() finished operating, the dtr callback is called, with private data supplied data argument. The devfs_clear_cdevpriv() function will be also be called if the open callback function returns an error code.

On the last filedescriptor close, system automatically arranges devfs_clear_cdevpriv() call.

If successful, the functions return 0.

The function devfs_set_cdevpriv() returns the following values on error:

[ENOENT]
    The current call is not associated with some filedescriptor.

[EBUSY]
    The private driver data is already associated with current filedescriptor.

The function devfs_get_cdevpriv() returns the following values on error:

[EBADF]
    The current call is not associated with some filedescriptor.

[ENOENT]
    The private driver data was not associated with current filedescriptor, or devfs_clear_cdevpriv() was called.

The function devfs_foreach_cdevpriv() sequentially calls the function cb for each cdevpriv structure, currently associated with the cdev device. The iterated cdevpriv data pointer and the user-supplied context arg are passed to the function cb. If cb returns non-zero value, the iteration stops on that element. The devfs_foreach_cdevpriv() returns the return value from the last call to cb, or zero if no cdevpriv data is currently associated with the device.

Current implementation of the iterator makes it impossible to use any blockable locking inside the callback cb.

SEE ALSO
close(2), open(2), devfs(4)

HISTORY
The devfs_cdevpriv() family of functions first appeared in FreeBSD 7.1.