vn_rdwr

Declaration

int vn_rdwr(enum uio_rw rw, struct vnode *vp, caddr_t base, int len, off_t offset, enum uio_seg segflg, int ioflg, kauth_cred_t cred, int *aresid, proc_t p);

Parameters

• rw:

  UIO_READ for a read, UIO_WRITE for a write.

• vp:

  The vnode on which to perform I/O.

• base:

  Start of buffer into which to read or from which to write data.

• len:

  Length of buffer.

• offset:

  Offset within the file at which to start I/O.

• segflg:

  What kind of address "base" is. See uio_seg definition in sys/uio.h. UIO_SYSSPACE for kernelspace, UIO_USERSPACE for userspace. UIO_USERSPACE32 and UIO_USERSPACE64 are in general preferred, but vn_rdwr will make sure that has the correct address sizes.

• ioflg:

  Defined in vnode.h, e.g. IO_NOAUTH, IO_NOCACHE.

• cred:

  Credential to pass down to filesystem for authentication.

• aresid:

  Destination for amount of requested I/O which was not completed, as with uio_resid().

• p:

  Process requesting I/O.

Return Value

0 for success; errors from filesystem, and EIO if did not perform all requested I/O and the "aresid" parameter is NULL.

Discussion

vn_rdwr() abstracts the details of constructing a uio and picking a vnode operation to allow simple in-kernel file I/O.