[Qemu-devel] Re: [PATCH 2/7] iohandlers: Introduce a new API

[Anthony Liguori <anthony@codemonkey.ws>]

On 02/22/2011 04:18 AM, Amit Shah wrote:
> Introduce a new iohandler api that doesn't have multiple callbacks.
> Instead, a single callback and a mask of events that got set will be
> passed on to the handler.  This will ease our transition to a poll()
> interface instead of the current select() that happens on the fds.
>
> Signed-off-by: Amit Shah<amit.shah@redhat.com>
> ---
>   iohandler.h |   28 +++++++++++
>   vl.c        |  144 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 172 insertions(+), 0 deletions(-)
>   create mode 100644 iohandler.h
>
> diff --git a/iohandler.h b/iohandler.h
> new file mode 100644
> index 0000000..6553835
> --- /dev/null
> +++ b/iohandler.h
> @@ -0,0 +1,28 @@
> +/*
> + * Declarations for iohandler functions
> + *
> + * Copyright Red Hat, Inc. 2011
> + * Copyright Amit Shah<amit.shah@redhat.com>  2011
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + */
> +
> +#ifndef _QEMU_IOHANDLER_H
> +#define _QEMU_IOHANDLER_H
> +
> +/* iohandler masks */
> +#define IOH_MASK_CAN_READ	(1U<<  0)
> +#define IOH_MASK_READ		(1U<<  1)
> +#define IOH_MASK_WRITE		(1U<<  2)
> +
> +typedef int IOAllHandler(void *opaque, unsigned int mask);
> +
> +int assign_iohandler(int fd, IOAllHandler *handler, unsigned int mask,
> +                     void *opaque);
> +int remove_iohandler(int fd);
> +int update_fd_mask(int fd, unsigned int mask);
> +int get_fd_mask(int fd, unsigned int *mask);
>    

As I previously suggested, we should return a connection handle instead 
of using an fd as an implicit handle.

Regards,

Anthony Liguori

> +
> +
> +#endif /* _QEMU_IOHANDLER_H */
> diff --git a/vl.c b/vl.c
> index e248ec4..9dabee2 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2,6 +2,8 @@
>    * QEMU System Emulator
>    *
>    * Copyright (c) 2003-2008 Fabrice Bellard
> + * Copyright (C) 2011 Red Hat, Inc.
> + * Copyright (C) 2011 Amit Shah,<amit.shah@redhat.com>
>    *
>    * Permission is hereby granted, free of charge, to any person obtaining a copy
>    * of this software and associated documentation files (the "Software"), to deal
> @@ -136,6 +138,7 @@ int main(int argc, char **argv)
>   #include "gdbstub.h"
>   #include "qemu-timer.h"
>   #include "qemu-char.h"
> +#include "iohandler.h"
>   #include "cache-utils.h"
>   #include "block.h"
>   #include "blockdev.h"
> @@ -1030,6 +1033,8 @@ typedef struct IOHandlerRecord {
>       IOCanReadHandler *fd_read_poll;
>       IOHandler *fd_read;
>       IOHandler *fd_write;
> +    IOAllHandler *fd_iohandler;
> +    unsigned int mask;
>       int deleted;
>       void *opaque;
>       /* temporary data */
> @@ -1040,6 +1045,97 @@ typedef struct IOHandlerRecord {
>   static QLIST_HEAD(, IOHandlerRecord) io_handlers_old =
>       QLIST_HEAD_INITIALIZER(io_handlers_old);
>
> +static QLIST_HEAD(, IOHandlerRecord) io_handlers =
> +    QLIST_HEAD_INITIALIZER(io_handlers);
> +
> +static IOHandlerRecord *find_iohandler(int fd)
> +{
> +    IOHandlerRecord *ioh;
> +
> +    QLIST_FOREACH(ioh,&io_handlers, next) {
> +        if (ioh->fd == fd) {
> +            return ioh;
> +        }
> +    }
> +    return NULL;
> +}
> +
> +static int update_iohandler_mask(IOHandlerRecord *ioh, unsigned int mask)
> +{
> +    assert(ioh);
> +
> +    ioh->mask = mask;
> +    return 0;
> +}
> +
> +/*
> + * Updates the mask for the fd.  Returns 0 on success.
> + */
> +int update_fd_mask(int fd, unsigned int mask)
> +{
> +    IOHandlerRecord *ioh;
> +
> +    ioh = find_iohandler(fd);
> +    if (!ioh) {
> +        return -1;
> +    }
> +
> +    return update_iohandler_mask(ioh, mask);
> +}
> +
> +/*
> + * Populates the mask registered in *mask.  Only valid if return value
> + * is 0.
> + */
> +int get_fd_mask(int fd, unsigned int *mask)
> +{
> +    IOHandlerRecord *ioh;
> +
> +    ioh = find_iohandler(fd);
> +    if (!ioh) {
> +        return -1;
> +    }
> +    *mask = ioh->mask;
> +
> +    return 0;
> +}
> +
> +/*
> + * Assign an iohandler to an fd.  Can also be used to update the mask
> + * or handler or the opaque pointer and also to delete the iohandler.
> + * Returns 0 on success.
> + */
> +int assign_iohandler(int fd, IOAllHandler *handler, unsigned int mask,
> +                     void *opaque)
> +{
> +    IOHandlerRecord *ioh;
> +
> +    ioh = find_iohandler(fd);
> +
> +    if (!handler) {
> +        if (ioh) {
> +            ioh->deleted = 1;
> +        }
> +        return 0;
> +    }
> +
> +    if (!ioh) {
> +        ioh = qemu_mallocz(sizeof(IOHandlerRecord));
> +        QLIST_INSERT_HEAD(&io_handlers, ioh, next);
> +        ioh->fd = fd;
> +    }
> +    ioh->fd_iohandler = handler;
> +    ioh->opaque = opaque;
> +    update_iohandler_mask(ioh, mask);
> +    ioh->deleted = 0;
> +
> +    return 0;
> +}
> +
> +int remove_iohandler(int fd)
> +{
> +    return assign_iohandler(fd, NULL, 0, NULL);
> +}
>
>   /* XXX: fd_read_poll should be suppressed, but an API change is
>      necessary in the character devices to suppress fd_can_read(). */
> @@ -1363,6 +1459,26 @@ void main_loop_wait(int nonblocking)
>                   nfds = ioh->fd;
>           }
>       }
> +    QLIST_FOREACH(ioh,&io_handlers, next) {
> +        if (ioh->deleted) {
> +            continue;
> +        }
> +        if (ioh->mask&  IOH_MASK_READ&&
> +            (!(ioh->mask&  IOH_MASK_CAN_READ) ||
> +             (ioh->fd_iohandler(ioh->opaque, IOH_MASK_CAN_READ) != 0))) {
> +
> +            FD_SET(ioh->fd,&rfds);
> +            if (ioh->fd>  nfds) {
> +                nfds = ioh->fd;
> +            }
> +        }
> +        if (ioh->mask&  IOH_MASK_WRITE) {
> +            FD_SET(ioh->fd,&wfds);
> +            if (ioh->fd>  nfds) {
> +                nfds = ioh->fd;
> +            }
> +        }
> +    }
>
>       tv.tv_sec = timeout / 1000;
>       tv.tv_usec = (timeout % 1000) * 1000;
> @@ -1389,6 +1505,34 @@ void main_loop_wait(int nonblocking)
>                   qemu_free(ioh);
>               }
>           }
> +        QLIST_FOREACH_SAFE(ioh,&io_handlers, next, pioh) {
> +            unsigned int mask;
> +
> +            mask = 0;
> +            if (!ioh->deleted) {
> +                if (FD_ISSET(ioh->fd,&rfds)) {
> +                    mask |= IOH_MASK_READ;
> +                }
> +                if (FD_ISSET(ioh->fd,&wfds)) {
> +                    mask |= IOH_MASK_WRITE;
> +                }
> +            }
> +            /*
> +             * Strip out flags the caller didn't ask for -- shouldn't
> +             * happen since we set rfds and wfds based on the value of
> +             * ioh->mask anyway.
> +             */
> +            mask&= ioh->mask;
> +            if (mask) {
> +                ioh->fd_iohandler(ioh->opaque, mask);
> +            }
> +            /* Do this last in case the handler marked it for deletion */
> +            if (ioh->deleted) {
> +                QLIST_REMOVE(ioh, next);
> +                qemu_free(ioh);
> +                continue;
> +            }
> +        }
>       }
>
>       slirp_select_poll(&rfds,&wfds,&xfds, (ret<  0));
>