The Design and Implementation of the Anykernel and Rump Kernels

161
int
p2k_node_read(struct puffs_usermount *pu, puffs_cookie_t opc,
uint8_t *buf, off_t offset, size_t *resid, const struct puffs_cred *pcr, int ioflag)
{
struct vnode *vp = OPC2VP(opc);
struct kauth_cred *cred = cred_create(pcr);
struct uio *uio = rump_pub_uio_setup(buf, *resid, offset, RUMPUIO_READ);
int rv;
RUMP_VOP_LOCK(vp, LK_SHARED);
rv = RUMP_VOP_READ(vp, uio, ioflag, cred);
RUMP_VOP_UNLOCK(vp);
*resid = rump_pub_uio_free(uio);
cred_destroy(cred);
}
return rv;
Figure 3.32: Implementation of p2k_node_read(). The parameters from the
puffs interface are translated to parameters expected by the kernel vnode interface.
Kernel data types are not exposed to userspace, so rump kernel public routines are
used to allocate, initialize and release such types.
ences a file using a struct vnode pointer, whereas puffs references one using a
puffs_cookie_t value. Another example of a difference is the way (address, size)-
tuples are indicated. In the kernel struct uio is used. In puffs, the same information
is passed as separate pointer and byte count parameters.
The p2k, or puffs-to-kernel, library is a request translator between the puffs userspace
file system interface and the kernel virtual file system interface (manual page p2k.3
at A–12). It also interprets the results from the kernel file systems and converts
them back to a format that puffs understands.
Most of the translation done by the p2k library is a matter of converting data
types back and forth. To give an example of p2k operation, we discuss reading a
file, which is illustrated by the p2k read routine in Figure 3.32. We see the uio