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

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

On 08/07/2012 02:16 PM, Stefan Hajnoczi wrote:
> On Fri, Aug 3, 2012 at 6:28 PM, Corey Bryant <coreyb@linux.vnet.ibm.com> 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