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NAME

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

SYNOPSIS

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

     typedef void (*cdevpriv_dtr_t)(void *data);

     int
     devfs_get_cdevpriv(void **datap);

     int
     devfs_set_cdevpriv(void *priv, cdevpriv_dtr_t dtr);

     void
     devfs_clear_cdevpriv(void);

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(5) 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.

     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.

SEE ALSO

     open(2), close(2), devfs(5), kern_openat(9)

HISTORY

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