Re: [Qemu-devel] [PATCH v9 6/7] block: Enable qemu_open/close to work with fd sets

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

I'll send a new version shortly with these updates also.

-- 
Regards,
Corey

On 08/11/2012 10:28 AM, Eric Blake wrote:
> On 08/11/2012 07:14 AM, Corey Bryant wrote:
>> When qemu_open is passed a filename of the "/dev/fdset/nnn"
>> format (where nnn is the fdset ID), an fd with matching access
>> mode flags will be searched for within the specified monitor
>> fd set.  If the fd is found, a dup of the fd will be returned
>> from qemu_open.
>>
>
>> v9:
>>   -Drop fdset refcount and check dup_fds instead. (eblake@redhat.com)
>>   -Fix dupfd leak in qemu_dup(). (eblake@redhat.com)
>>   -Always set O_CLOEXEC in qemu_dup(). (kwolf@redhat.com)
>>   -Change name of qemu_dup() to qemu_dup_flags(). (kwolf@redhat.com)
>>
>
>> @@ -87,6 +146,40 @@ int qemu_open(const char *name, int flags, ...)
>>       int ret;
>>       int mode = 0;
>>
>> +#ifndef _WIN32
>> +    const char *fdset_id_str;
>> +
>> +    /* Attempt dup of fd from fd set */
>> +    if (strstart(name, "/dev/fdset/", &fdset_id_str)) {
>> +        int64_t fdset_id;
>> +        int fd, dupfd;
>> +
>> +        fdset_id = qemu_parse_fdset(fdset_id_str);
>> +        if (fdset_id == -1) {
>> +            errno = EINVAL;
>> +            return -1;
>> +        }
>> +
>> +        fd = monitor_fdset_get_fd(fdset_id, flags);
>> +        if (fd == -1) {
>> +            return -1;
>> +        }
>> +
>> +        dupfd = qemu_dup_flags(fd, flags);
>> +        if (fd == -1) {
>
> Checking the wrong condition:
> s/fd/dupfd/
>
>> +            return -1;
>> +        }
>> +
>> +        ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
>> +        if (ret == -1) {
>> +            close(dupfd);
>> +            return -1;
>
> This function appears to promise a reasonable errno on failure.
> However, I don't think monitor_fdset_dup_fd_add guarantees a reasonable
> errno, and even if it does, close() can corrupt errno.  I think that
> prior to returning here, you either need an explicit errno=ENOMEM, or
> fix monitor_fdset_dup_fd to guarantee a nice errno, plus a save and
> restore of errno here.  Unless no one cares about errno on failure, in
> which case your earlier errno=EINVAL can be dropped.
>

-- 
Regards,
Corey