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Date: Thu, 25 Oct 2012 09:25:35 +0200 (CEST)
From: Alexandre DERUMIER <aderumier@odiso.com>
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Subject: [Qemu-devel] qemu-img convert with block driver without
	.bdrv_create (like iscsi)
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To: qemu-devel <qemu-devel@nongnu.org>
Cc: kwolf@redhat.com, pbonzini@redhat.com, ronnie sahlberg <ronniesahlberg@gmail.com>

Hello,

I'm looking to use qemu-img convert to write to iscsi block device (iscsi://..)

As iscsi doesn't have  .bdrv_create, qemu-img convert hang on 


    /* Create the new image */
    ret = bdrv_create(drv, out_filename, param);
    if (ret < 0) {
        if (ret == -ENOTSUP) {
            error_report("Formatting not supported for file format '%s'",
                         out_fmt);
        } else if (ret == -EFBIG) {
            error_report("The image size is too large for file format '%s'",
                         out_fmt);
        } else {
            error_report("%s: error while converting %s: %s",
                         out_filename, out_fmt, strerror(-ret));
        }
        goto out;
    }




What is the best way to get it working ?


1)add a .bdrv_create in block/iscsi.c ? 

(like host_device block driver, only open/close the device and check if size if big enough)

block/raw-posix.c
.bdrv_create        = hdev_create,

static int hdev_create(const char *filename, QEMUOptionParameter *options)
{
    int fd;
    int ret = 0;
    struct stat stat_buf;
    int64_t total_size = 0;

    /* Read out options */
    while (options && options->name) {
        if (!strcmp(options->name, "size")) {
            total_size = options->value.n / BDRV_SECTOR_SIZE;
        }
        options++;
    }

    fd = qemu_open(filename, O_WRONLY | O_BINARY);
    if (fd < 0)
        return -errno;

    if (fstat(fd, &stat_buf) < 0)
        ret = -errno;
    else if (!S_ISBLK(stat_buf.st_mode) && !S_ISCHR(stat_buf.st_mode))
        ret = -ENODEV;
    else if (lseek(fd, 0, SEEK_END) < total_size * BDRV_SECTOR_SIZE)
        ret = -ENOSPC;

    qemu_close(fd);
    return ret;
}


2)or add a fallback in qemu-img, if bdrv_create doesn't exist, use bdrv_open to see if the backend device is pre-existing ?


Regards,

Alexandre Derumier