Re: [PATCH 1/2] tools/libs/evtchn: decouple more from mini-os

[Andrew Cooper <amc96@xxxxxxxx>]

On 07/01/2022 10:35, Juergen Gross wrote:
> diff --git a/tools/libs/evtchn/minios.c b/tools/libs/evtchn/minios.c
> index e5dfdc5ef5..3305102f22 100644
> --- a/tools/libs/evtchn/minios.c
> +++ b/tools/libs/evtchn/minios.c
> @@ -38,16 +38,27 @@
>  
>  #include "private.h"
>  
> +LIST_HEAD(port_list, port_info);
> +
> +struct port_info {
> +    LIST_ENTRY(port_info) list;
> +    evtchn_port_t port;
> +    unsigned long pending;
> +    int bound;

Now this is private, it's even more clear that pending and bound are bool's.

Making this adjustment drops 16 bytes from the structure.

> +};
> +
>  extern void minios_evtchn_close_fd(int fd);
>  
>  extern struct wait_queue_head event_queue;
>  
>  /* XXX Note: This is not threadsafe */
> -static struct evtchn_port_info *port_alloc(int fd)
> +static struct port_info *port_alloc(int fd)
>  {
> -    struct evtchn_port_info *port_info;
> +    struct port_info *port_info;
> +    struct file *file = get_file_from_fd(fd);
> +    struct port_list *port_list = file->dev;

This would be rather more obviously correct if port_alloc() took xce
rather than fd.

It is reasonable to assume that xce->fd is good, and that
get_file_from_fd(xce->fd) will be non-null, but the current logic makes
this very opaque.

> @@ -75,12 +86,25 @@ static void port_dealloc(struct evtchn_port_info 
> *port_info)
>   */
>  int osdep_evtchn_open(xenevtchn_handle *xce, unsigned int flags)
>  {
> -    int fd = alloc_fd(FTYPE_EVTCHN);
> +    int fd;
> +    struct file *file;
> +    struct port_list *list;
> +
> +    list = malloc(sizeof(*list));
> +    if ( !list )
> +        return -1;
> +
> +    fd = alloc_fd(FTYPE_EVTCHN);
> +    file = get_file_from_fd(fd);
>  
> -    if ( fd == -1 )
> +    if ( !file )
> +    {
> +        free(list);
>          return -1;
> +    }

This wants rearranging to keep alloc_fd() ahead of malloc().  With that,
there is no need for free(list) in this error path.

>  
> -    LIST_INIT(&files[fd].evtchn.ports);
> +    file->dev = list;
> +    LIST_INIT(list);
>      xce->fd = fd;
>      printf("evtchn_open() -> %d\n", fd);
>  
> @@ -104,12 +128,15 @@ int osdep_evtchn_restrict(xenevtchn_handle *xce, 
> domid_t domid)
>  
>  void minios_evtchn_close_fd(int fd)

Something very broken is going on here.  The top of evtchn.c declares:

extern void minios_evtchn_close_fd(int fd);

I'm surprised that the compiler doesn't object to instantiating a
function which has previously been declared extern.


Furthermore, in minios itself.

lib/sys.c:91:extern void minios_evtchn_close_fd(int fd);
lib/sys.c:447:      minios_evtchn_close_fd(fd);

So lib/sys.c locally extern's this function too.  It needs to be in the
public API if it is used like this, but surely the better thing is to
wire up xenevtchn_close() properly.

>  {
> -    struct evtchn_port_info *port_info, *tmp;
> +    struct port_info *port_info, *tmp;
> +    struct file *file = get_file_from_fd(fd);
> +    struct port_list *port_list = file->dev;

Is it safe to assume that fd is good here?

> @@ -273,15 +305,17 @@ xenevtchn_port_or_error_t 
> xenevtchn_bind_virq(xenevtchn_handle *xce,
>  xenevtchn_port_or_error_t xenevtchn_pending(xenevtchn_handle *xce)
>  {
>      int fd = xce->fd;
> -    struct evtchn_port_info *port_info;
> +    struct file *file = get_file_from_fd(fd);

You've dropped all uses of 'fd' from this function, so why not drop the
local variable and use xce->fd here?

~Andrew