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Full Discussion: Entry Points Routine
Top Forums Programming Entry Points Routine Post 29783 by Perderabo on Friday 11th of October 2002 09:00:53 AM
Old 10-11-2002
Quote:
Originally posted by S.P.Prasad
I just cannot figure it out then why,as I have stated "The declaration within the table contains information in the structure "see dev switch" has a member variable of type pointer to struct streamtab.
As far as I know, it doesn't; and you are in error if you think it does. Here is cdevsw from HP-UX 11.0:
Code:
 
/*
 * Character device switch.
 */
struct cdevsw
{
        d_open_t        d_open;
        d_close_t       d_close;
        d_read_t        d_read;
        d_write_t       d_write;
        d_ioctl_t       d_ioctl;
        d_select_t      d_select;
        d_option1_t     d_option1;
        int             d_flags;       /* C_MGR_IS_MP is valid for this field */
        void            *d_drv_info;
        pfilter_t       *d_pfilter_s;
        aio_ops_t       *d_aio_ops;
};

To use d_read as an example, The type of d_read is:
typedef int (*d_read_t) __((dev_t dev, struct uio *uio));
And that typedef does not magically change into a pointer to a qinit structure if the current entry happens to be a streams based driver. Any time the read or readv system call invokes the read routine of a character driver, that read routine is passed a device and a uio structure. Every read of a character device is treated this way. No there no exception for streams-based character drivers.

The cdevsw for osf1 is similiar but with much less type checking:
Code:
struct cdevsw
{
        int     (*d_open)();
        int     (*d_close)();
        int     (*d_read)();
        int     (*d_write)();
        int     (*d_ioctl)();
        int     (*d_stop)();
        int     (*d_reset)();
        struct tty *d_ttys;
        int     (*d_select)();
        int     (*d_mmap)();
        int     d_funnel;       /* serial code compatibility */
        int     (*d_segmap)();          /* xxx_segmap() entry point */
        int     d_flags;                /* if (C_DDIDKI), driver follows
                                           SVR4 DDI/DKI interfaces*/
};

Without strong typechecking it's hard to prove exactly what d_read is. But that DDI/DKI stands for Device Driver Interface/Driver Kernel Interface. You can be sure that a system that supports that standard is not going to turn d_read into a pointer to a qinit structure.

If you post again claiming that your cdevsw has pointers to qinit (or other stream) structures, please also post some evidence as well. I would also like to know which stream structure you think that your d_ioctl points to.
 

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LEARN ABOUT CENTOS

strategy

strategy(9E)							Driver Entry Points						      strategy(9E)

NAME

       strategy - perform block I/O

SYNOPSIS

       #include <sys/types.h>
       #include <sys/buf.h>
       #include <sys/ddi.h>
       #include <sys/sunddi.h>

       int prefixstrategy(struct buf *bp);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI). This entry point is required for block devices.

PARAMETERS

       bp	Pointer to the buf(9S) structure.

DESCRIPTION

       The strategy() routine is called indirectly (through cb_ops(9S)) by the kernel to read and write blocks of data on the block device. strat-
       egy() may also be called directly or indirectly to support the  raw  character  interface  of  a  block	device	(read(9E),  write(9E)  and
       ioctl(9E)). The strategy() routine's responsibility is to set up and initiate the transfer.

       In  general, strategy() should not block. It can, however, perform a kmem_cache_alloc(9F) with both the KM_PUSHPAGE and KM_SLEEP flags set,
       which might block, without causing deadlock in low memory situations.

RETURN VALUES

       The strategy() function must return 0. On an error condition, it should call bioerror(9f) to set b_flags to the proper error code, and call
       biodone(9f). Note that a partial transfer is not considered to be an error.

SEE ALSO

       ioctl(9E), read(9E), write(9E), biodone(9F), bioerror(9F), buf(9S), cb_ops(9S), kmem_cache_alloc(9F)

       Writing Device Drivers

SunOS 5.10							    6 Nov 2003							      strategy(9E)
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