Re: [Qemu-devel] [PATCH v6 2/6] qapi: Introduce add-fd, remove-fd, query-fdsets

[Corey Bryant]

On 08/07/2012 02:16 PM, Stefan Hajnoczi wrote:
> On Fri, Aug 3, 2012 at 6:28 PM, Corey Bryant <address@hidden> wrote:
> > diff --git a/monitor.c b/monitor.c
> > index 49dccfe..9aa9f7e 100644
> > --- a/monitor.c
> > +++ b/monitor.c
> > @@ -140,6 +140,24 @@ struct mon_fd_t {
> >       QLIST_ENTRY(mon_fd_t) next;
> >   };
> >
> > +/* file descriptor associated with a file descriptor set */
> > +typedef struct mon_fdset_fd_t mon_fdset_fd_t;
> > +struct mon_fdset_fd_t {
>
> QEMU coding style is:
>
> typedef struct MonFdsetFd MonFdsetFd;
> struct MonFdsetFd {
>
> See ./CODING_STYLE for more info.

Thanks, I'll fix that.

> > +    int fd;
> > +    bool removed;
> > +    QLIST_ENTRY(mon_fdset_fd_t) next;
> > +};
> > +
> > +/* file descriptor set containing fds passed via SCM_RIGHTS */
> > +typedef struct mon_fdset_t mon_fdset_t;
> > +struct mon_fdset_t {
> > +    int64_t id;
> > +    int refcount;
> > +    bool in_use;
> > +    QLIST_HEAD(, mon_fdset_fd_t) fds;
> > +    QLIST_ENTRY(mon_fdset_t) next;
> > +};
>
> At this point in the patch series it's not clear to me whether the
> removed and refcount/in_use fields are a clean and correct solution.
> Exposing these fields via QMP is also something I'm going to carefully
> review because they seem like internals.

Yes, please review the v7 patches and let me know what you think.  I 
explained the purpose of these fields in the previous email I just sent 
you, so I won't go into their details again here.  But I will point out 
that refcount/in-use came about after concern of fd leakage if libvirt's 
monitor connection disconnects.  query-fdsets allows the client to 
determine the state of the fd sets after reconnecting.

> > +
> >   typedef struct MonitorControl {
> >       QObject *id;
> >       JSONMessageParser parser;
> > @@ -176,7 +194,8 @@ struct Monitor {
> >       int print_calls_nr;
> >   #endif
> >       QError *error;
> > -    QLIST_HEAD(,mon_fd_t) fds;
> > +    QLIST_HEAD(, mon_fd_t) fds;
> > +    QLIST_HEAD(, mon_fdset_t) fdsets;
> >       QLIST_ENTRY(Monitor) entry;
> >   };
> >
> > @@ -2389,6 +2408,157 @@ int monitor_get_fd(Monitor *mon, const char *fdname)
> >       return -1;
> >   }
> >
> > +static void monitor_fdset_cleanup(mon_fdset_t *mon_fdset)
> > +{
> > +    mon_fdset_fd_t *mon_fdset_fd;
> > +    mon_fdset_fd_t *mon_fdset_fd_next;
> > +
> > +    if (mon_fdset->refcount != 0) {
> > +        return;
> > +    }
> > +
> > +    QLIST_FOREACH_SAFE(mon_fdset_fd, &mon_fdset->fds, next, mon_fdset_fd_next) 
> > {
> > +        if (!mon_fdset->in_use || mon_fdset_fd->removed) {
> > +            close(mon_fdset_fd->fd);
> > +            QLIST_REMOVE(mon_fdset_fd, next);
> > +            g_free(mon_fdset_fd);
> > +        }
> > +    }
> > +
> > +    if (QLIST_EMPTY(&mon_fdset->fds)) {
> > +        QLIST_REMOVE(mon_fdset, next);
> > +        g_free(mon_fdset);
> > +    }
> > +}
> > +
> > +AddfdInfo *qmp_add_fd(bool has_fdset_id, int64_t fdset_id, Error **errp)
> > +{
> > +    int fd;
> > +    Monitor *mon = cur_mon;
> > +    mon_fdset_t *mon_fdset;
> > +    mon_fdset_fd_t *mon_fdset_fd;
> > +    AddfdInfo *fdinfo;
> > +
> > +    fd = qemu_chr_fe_get_msgfd(mon->chr);
> > +    if (fd == -1) {
> > +        qerror_report(QERR_FD_NOT_SUPPLIED);
> > +        return NULL;
> > +    }
> > +
> > +    if (has_fdset_id) {
> > +        QLIST_FOREACH(mon_fdset, &mon->fdsets, next) {
> > +            if (mon_fdset->id == fdset_id) {
> > +                break;
> > +            }
> > +        }
> > +        if (mon_fdset == NULL) {
> > +            qerror_report(QERR_FDSET_NOT_FOUND, fdset_id);
> > +            return NULL;
>
> fd is leaked?

Yes, it looks like it is.  I'll fix that.

> > +        }
> > +    } else {
> > +        int64_t fdset_id_prev = -1;
> > +        mon_fdset_t *mon_fdset_cur = QLIST_FIRST(&mon->fdsets);
> > +
> > +        /* Use first available fdset ID */
> > +        QLIST_FOREACH(mon_fdset, &mon->fdsets, next) {
> > +            mon_fdset_cur = mon_fdset;
> > +            if (fdset_id_prev == mon_fdset_cur->id - 1) {
> > +                fdset_id_prev = mon_fdset_cur->id;
> > +                continue;
> > +            }
> > +            break;
> > +        }
> > +
> > +        mon_fdset = g_malloc0(sizeof(*mon_fdset));
> > +        mon_fdset->id = fdset_id_prev + 1;
> > +        mon_fdset->refcount = 0;
> > +        mon_fdset->in_use = true;
> > +
> > +        /* The fdset list is ordered by fdset ID */
> > +        if (mon_fdset->id == 0) {
> > +            QLIST_INSERT_HEAD(&mon->fdsets, mon_fdset, next);
> > +        } else if (mon_fdset->id < mon_fdset_cur->id) {
> > +            QLIST_INSERT_BEFORE(mon_fdset_cur, mon_fdset, next);
> > +        } else {
> > +            QLIST_INSERT_AFTER(mon_fdset_cur, mon_fdset, next);
> > +        }
> > +    }
> > +
> > +    mon_fdset_fd = g_malloc0(sizeof(*mon_fdset_fd));
> > +    mon_fdset_fd->fd = fd;
> > +    mon_fdset_fd->removed = false;
> > +    QLIST_INSERT_HEAD(&mon_fdset->fds, mon_fdset_fd, next);
> > +
> > +    fdinfo = g_malloc0(sizeof(*fdinfo));
> > +    fdinfo->fdset_id = mon_fdset->id;
> > +    fdinfo->fd = mon_fdset_fd->fd;
> > +
> > +    return fdinfo;
> > +}
> > +
> > +void qmp_remove_fd(int64_t fdset_id, bool has_fd, int64_t fd, Error **errp)
> > +{
> > +    Monitor *mon = cur_mon;
> > +    mon_fdset_t *mon_fdset;
> > +    mon_fdset_fd_t *mon_fdset_fd;
> > +    char fd_str[20];
> > +
> > +    QLIST_FOREACH(mon_fdset, &mon->fdsets, next) {
> > +        if (mon_fdset->id != fdset_id) {
> > +            continue;
> > +        }
> > +        QLIST_FOREACH(mon_fdset_fd, &mon_fdset->fds, next) {
> > +            if (has_fd && mon_fdset_fd->fd != fd) {
> > +                continue;
> > +            }
> > +            mon_fdset_fd->removed = true;
> > +            if (has_fd) {
> > +                break;
> > +            }
> > +        }
> > +        monitor_fdset_cleanup(mon_fdset);
> > +        return;
> > +    }
> > +    snprintf(fd_str, sizeof(fd_str), "%ld", fd);
> > +    qerror_report(QERR_FD_NOT_FOUND, fd_str);
>
> Why use an fd_str instead of passing an int64_t into the error
> message?  This also assumed sizeof(long) == 8, which isn't true on
> 32-bit hosts, so %ld should be %"PRId64".

Can I pass an int64_t into the message if it takes a string?

I thought int64_t was a long long in 32-bit mode, but perhaps that's not 
always the case?

> There is a new policy on error reporting.  I think this patch series
> may be affected/conflict, please qemu-devel to check.  I think Luiz
> can also help here.

Ok thanks, I'll take a look at qemu-devel.

--
Regards,
Corey