Re: [Qemu-devel] [PATCH] block: add native support for NFS

[Peter Lieven <pl@kamp.de>]

On 17.12.2013 09:51, Fam Zheng wrote:
> 于2013年 12月17日 星期二 16时46分50秒,Peter Lieven写到:
>> On 17.12.2013 09:29, Fam Zheng wrote:
>>> On 2013年12月17日 15:53, Peter Lieven wrote:
>>>> Hi Fam,
>>>>
>>>> On 17.12.2013 05:07, Fam Zheng wrote:
>>>>> On 2013年12月16日 23:34, Peter Lieven wrote:
>>>>>> +static int coroutine_fn nfs_co_writev(BlockDriverState *bs,
>>>>>> +                                        int64_t sector_num, int
>>>>>> nb_sectors,
>>>>>> +                                        QEMUIOVector *iov)
>>>>>> +{
>>>>>> +    nfsclient *client = bs->opaque;
>>>>>> +    struct NFSTask Task;
>>>>>> +    char *buf = NULL;
>>>>>> +
>>>>>> +    nfs_co_init_task(client, &Task);
>>>>>> +
>>>>>> +    buf = g_malloc(nb_sectors * BDRV_SECTOR_SIZE);
>>>>>> +    qemu_iovec_to_buf(iov, 0, buf, nb_sectors * BDRV_SECTOR_SIZE);
>>>>>> +
>>>>>> +    if (nfs_pwrite_async(client->context, client->fh,
>>>>>> +                         sector_num * BDRV_SECTOR_SIZE,
>>>>>> +                         nb_sectors * BDRV_SECTOR_SIZE,
>>>>>> +                         buf, nfs_co_generic_cb, &Task) != 0) {
>>>>>> +        g_free(buf);
>>>>>> +        return -EIO;
>>>>>> +    }
>>>>>> +
>>>>>> +    while (!Task.complete) {
>>>>>> +        nfs_set_events(client);
>>>>>> +        qemu_coroutine_yield();
>>>>>> +    }
>>>>>> +
>>>>>> +    g_free(buf);
>>>>>> +
>>>>>> +    if (Task.status != nb_sectors * BDRV_SECTOR_SIZE) {
>>>>>> +        return -EIO;
>>>>>> +    }
>>>>>> +
>>>>>> +    bs->total_sectors = MAX(bs->total_sectors, sector_num +
>>>>>> nb_sectors);
>>>>>> +    client->allocated_file_size = -ENOTSUP;
>>>>>
>>>>> Why does allocated_file_size become not supported after a write?
>>>> I thought that someone would ask this ;-) bdrv_allocated_file_size
>>>> is only
>>>> used in image info. I saved some code here implementing an async call.
>>>> On open I fstat anyway and store that value. For qemu-img info this is
>>>> sufficient, but the allocated size likely changes after a write.
>>>> -ENOTSUP
>>>> is the default if bdrv_allocated_file_size is not implemented.
>>>
>>> OK. Please add some comment here.
>>>
>>>>>> +static int nfs_file_open_common(BlockDriverState *bs, QDict
>>>>>> *options, int flags,
>>>>>> +                         int open_flags, Error **errp)
>>>>>> +{
>>>>>> +    nfsclient *client = bs->opaque;
>>>>>> +    const char *filename;
>>>>>> +    int ret = 0;
>>>>>> +    QemuOpts *opts;
>>>>>> +    Error *local_err = NULL;
>>>>>> +    char *server = NULL, *path = NULL, *file = NULL, *strp;
>>>>>> +    struct stat st;
>>>>>> +
>>>>>> +    opts = qemu_opts_create_nofail(&runtime_opts);
>>>>>> +    qemu_opts_absorb_qdict(opts, options, &local_err);
>>>>>> +    if (error_is_set(&local_err)) {
>>>>>> +        qerror_report_err(local_err);
>>>>>> +        error_free(local_err);
>>>>>> +        ret = -EINVAL;
>>>>>> +        goto fail;
>>>>>> +    }
>>>>>> +
>>>>>> +    filename = qemu_opt_get(opts, "filename");
>>>>>> +
>>>>>> +    client->context = nfs_init_context();
>>>>>> +
>>>>>> +    if (client->context == NULL) {
>>>>>> +        error_setg(errp, "Failed to init NFS context");
>>>>>> +        ret = -EINVAL;
>>>>>> +        goto fail;
>>>>>> +    }
>>>>>> +
>>>>>> +    server = g_strdup(filename + 6);
>>>>>
>>>>> Please check the length of filename is longer than 6 before accessing
>>>>> filename[6].
>>>> Good point. I will check for this, but in fact I think it can't happen
>>>> because we will
>>>> never end up there if filename does not start with nfs://
>>>
>>> True, at least for now, but it doesn't hurt to be defensive,
>>> especially with strings.
>>>
>>>>>
>>>>>> +    if (server[0] == '/' || server[0] == '\0') {
>>>>>> +        error_setg(errp, "Invalid server in URL");
>>>>>> +        ret = -EINVAL;
>>>>>> +        goto fail;
>>>>>> +    }
>>>>>> +    strp = strchr(server, '/');
>>>>>> +    if (strp == NULL) {
>>>>>> +        error_setg(errp, "Invalid URL specified.\n");
>>>>>> +        ret = -EINVAL;
>>>>>> +        goto fail;
>>>>>> +    }
>>>>>> +    path = g_strdup(strp);
>>>>>> +    *strp = 0;
>>>>>> +    strp = strrchr(path, '/');
>>>>>> +    if (strp == NULL) {
>>>>>> +        error_setg(errp, "Invalid URL specified.\n");
>>>>>> +        ret = -EINVAL;
>>>>>> +        goto fail;
>>>>>> +    }
>>>>>> +    file = g_strdup(strp);
>>>>>> +    *strp = 0;
>>>>>> +
>>>>>> +    if (nfs_mount(client->context, server, path) != 0) {
>>>>>> +        error_setg(errp, "Failed to mount nfs share: %s",
>>>>>> +                    nfs_get_error(client->context));
>>>>>> +        ret = -EINVAL;
>>>>>> +        goto fail;
>>>>>> +    }
>>>>>> +
>>>>>> +    if (open_flags & O_CREAT) {
>>>>>> +        if (nfs_creat(client->context, file, 0600, &client->fh)
>>>>>> != 0) {
>>>>>> +            error_setg(errp, "Failed to create file: %s",
>>>>>> + nfs_get_error(client->context));
>>>>>> +            ret = -EINVAL;
>>>>>> +            goto fail;
>>>>>> +        }
>>>>>> +    } else {
>>>>>> +        open_flags = (flags & BDRV_O_RDWR) ? O_RDWR : O_RDONLY;
>>>>>> +        if (nfs_open(client->context, file, open_flags, &client->fh)
>>>>>> != 0) {
>>>>>> +            error_setg(errp, "Failed to open file : %s",
>>>>>> + nfs_get_error(client->context));
>>>>>> +            ret = -EINVAL;
>>>>>> +            goto fail;
>>>>>> +        }
>>>>>> +    }
>>>>>> +
>>>>>> +    if (nfs_fstat(client->context, client->fh, &st) != 0) {
>>>>>> +        error_setg(errp, "Failed to fstat file: %s",
>>>>>> +                   nfs_get_error(client->context));
>>>>>> +        ret = -EIO;
>>>>>> +        goto fail;
>>>>>> +    }
>>>>>> +
>>>>>> +    bs->total_sectors = st.st_size / BDRV_SECTOR_SIZE;
>>>>>
>>>>> Please use DIV_ROUND_UP(). Otherwise the remainder in last sector
>>>>> couldn't be read.
>>>> Will do. Can't it happen that we end up reading unallocated sectors?
>>>
>>> Hmm, maybe. Not missing last bytes of unaligned sector is essential
>>> for VMDK description file. But you are right, please add check code
>>> and make sure that we don't read beyond EOF as well.
>> Actually it would like to keep bs->total_sectors = st.st_size /
>> BDRV_SECTOR_SIZE; for now until I have checked how libnfs and the
>> whole stack react on beyond EOF reads.
>>
>
> You don't need to care about libnfs' EOF behavior, nfs_pread_async is in bytes granularity, you could just read the last partial sector till EOF and zero padding the buffer.
isn't this something that is already in bdrv_co_do_readv?

do you have an example of an VMDK with descriptor file for me. I would try the implementation then.

Peter