segmap() Entry Point

int xxsegmap(dev_t dev, off_t off, struct as *asp, caddr_t *addrp,
     off_t len, unsigned int prot, unsigned int maxprot,
     unsigned int flags, cred_t *credp);

segmap(9E) is the entry point responsible for actually setting up a memory mapping requested by the system on behalf of an mmap(2) system call. Drivers for many memory-mapped devices will use ddi_devmap_segmap(9F) as the entry point rather than defining their own segmap(9E) routine.

If a driver wants to check mapping permissions or allocate private mapping resources before setting up the mapping, the driver can provide its own segmap(9E) entry point. segmap(9E) must call devmap_setup(9F) before returning.

In Example 10–10, the driver controls a frame buffer that allows write-only mappings. The driver returns EINVAL if the application tries to gain read access and then calls devmap_setup(9F) to set up the user mapping.

Example 10–10 segmap(9E) Routine

static int
xxsegmap(dev_t dev, off_t off, struct as *asp, caddr_t *addrp,
    off_t len, unsigned int prot, unsigned int maxprot,
    unsigned int flags, cred_t *credp)
{
        if (prot & PROT_READ)
                return (EINVAL);
        return (devmap_setup(dev, (offset_t)off, as, addrp,
            (size_t)len, prot, maxprot, flags, cred));
}