This patch implements the server part of readdir() implementation for
9p2000.L

    SYNOPSIS

    size[4] Treaddir tag[2] fid[4] offset[8] count[4]
    size[4] Rreaddir tag[2] count[4] data[count]

    DESCRIPTION

    The readdir request asks the server to read the directory specified by 'fid'
    at an offset specified by 'offset' and return as many dirent structures as
    possible that fit into count bytes. Each dirent structure is laid out as
    follows.

            qid.type[1]
              the type of the file (directory, etc.), represented as a bit
              vector corresponding to the high 8 bits of the file's mode
              word.

            qid.vers[4]
              version number for given path

            qid.path[8]
              the file server's unique identification for the file

            offset[8]
              offset into the next dirent.

            type[1]
              type of this directory entry.

            name[256]
              name of this directory entry.
Signed-off-by: NSripathi Kodi <sripathik@in.ibm.com>
Reviewed-by: NM. Mohan Kumar <mohan@in.ibm.com>
Signed-off-by: NVenkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>

While running in debug mode if 9P server is unable to open the log file
it results in a SEGV deep down in glibc:

Program received signal SIGSEGV, Segmentation fault.
0x008fca8c in fwrite () from /lib/libc.so.6
(gdb) bt
#0  0x008fca8c in fwrite () from /lib/libc.so.6
#1  0x081eb87e in pprint_pdu (pdu=0x89a52e1c)
    at /data/sripathi/code/qemu/new/qemu-next-upstream/hw/virtio-9p-debug.c:380
#2  0x0806dad8 in submit_pdu (s=0x897dc008, pdu=0x89a52e1c)
    at /data/sripathi/code/qemu/new/qemu-next-upstream/hw/virtio-9p.c:3092
#3  0x0806dc63 in handle_9p_output (vdev=0x897dc008, vq=0x86d8218)
    at /data/sripathi/code/qemu/new/qemu-next-upstream/hw/virtio-9p.c:3122
#4  0x081ac728 in virtio_queue_notify (vdev=0x897dc008, n=0)
    at /data/sripathi/code/qemu/new/qemu-next-upstream/hw/virtio.c:563
#5  0x08063876 in virtio_ioport_write (opaque=0x86d7b98, addr=16, val=0)
    at /data/sripathi/code/qemu/new/qemu-next-upstream/hw/virtio-pci.c:222
#6  0x08063e26 in virtio_pci_config_writew (opaque=0x86d7b98, addr=16, val=0)
    at /data/sripathi/code/qemu/new/qemu-next-upstream/hw/virtio-pci.c:357
#7  0x080c881a in ioport_write (index=1, address=49296, data=0) at ioport.c:80
#8  0x080c8d4c in cpu_outw (addr=49296, val=0) at ioport.c:204
#9  0x08073010 in kvm_handle_io (port=49296, data=0xab393000, direction=1, size=2, count=1)
    at /data/sripathi/code/qemu/new/qemu-next-upstream/kvm-all.c:735
...
...

This is ugly and misleading. The following patch adds a BUG_ON to catch this
error. With this patch we get an abort message like the following, which makes
it easier to analyze:

f12-kvm login: qemu: /data/sripathi/code/qemu/new/qemu-next-upstream/hw/virtio-9p-debug.c:353: pprint_pdu: Assertion `!(!llogfile)' failed.
Signed-off-by: NSripathi Kodi <sripathik@in.ibm.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

This patch fluesh the debug messages to the log file  at the end of each
debug message.

Changes from V1:
Used fflush instead fseek for the flush.
Signed-off-by: NVenkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

This patch doesn't implement the 9p protocol handling
code. It adds a simple device which dump the protocol data.

[jvrao@linux.vnet.ibm.com: Little-Endian to host format conversion]
[aneesh.kumar@linux.vnet.ibm.com: Multiple-mounts support]
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>