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

[Fam Zheng <famz@redhat.com>]

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.

Fam