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

[Alon Levy]

On Tue, Feb 22, 2011 at 03:48:31PM +0530, 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.
> 

Is the mask argument to the callback indicative of a real mask, or is
this an enum when passed to the clients? i.e. you seem to use a switch
in all handlers, so is it actually meant that each callback has a single
possible value, not an or'ed one?

> Signed-off-by: Amit Shah <address@hidden>
> ---
>  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 <address@hidden> 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);
> +
> +
> +#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, <address@hidden>
>   *
>   * 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));
> -- 
> 1.7.4
> 
>