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Re: [Qemu-devel] [PATCH for-4.1 1/2] fdc: Fix inserting read-only media
From: |
John Snow |
Subject: |
Re: [Qemu-devel] [PATCH for-4.1 1/2] fdc: Fix inserting read-only media in empty drive |
Date: |
Tue, 30 Jul 2019 11:24:17 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 |
On 7/30/19 10:57 AM, Kevin Wolf wrote:
> In order to insert a read-only medium (i.e. a read-only block node) to
> the BlockBackend of a floppy drive, we must not have taken write
> permissions on that BlockBackend, or the operation will fail with the
> error message "Block node is read-only".
>
> The device already takes care to remove all permissions when the medium
> is ejected, but the state isn't correct if the drive is initially empty:
> It uses blk_is_read_only() to check whether write permissions should be
> taken, but this function returns false for empty BlockBackends in the
> common case.
>
> Fix floppy_drive_realize() to avoid taking write permissions if the
> drive is empty.
>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
> hw/block/fdc.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/hw/block/fdc.c b/hw/block/fdc.c
> index 77af9979de..9b24cb9b85 100644
> --- a/hw/block/fdc.c
> +++ b/hw/block/fdc.c
> @@ -514,6 +514,7 @@ static void floppy_drive_realize(DeviceState *qdev, Error
> **errp)
> FloppyDrive *dev = FLOPPY_DRIVE(qdev);
> FloppyBus *bus = FLOPPY_BUS(qdev->parent_bus);
> FDrive *drive;
> + bool read_only;
> int ret;
>
> if (dev->unit == -1) {
> @@ -542,6 +543,12 @@ static void floppy_drive_realize(DeviceState *qdev,
> Error **errp)
> dev->conf.blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL);
> ret = blk_attach_dev(dev->conf.blk, qdev);
> assert(ret == 0);
> +
> + /* Don't take write permissions on an empty drive to allow attaching
> a
> + * read-only node later */
> + read_only = true;
> + } else {
> + read_only = !blk_bs(dev->conf.blk) ||
> blk_is_read_only(dev->conf.blk);
> }
>
> blkconf_blocksizes(&dev->conf);
> @@ -559,9 +566,7 @@ static void floppy_drive_realize(DeviceState *qdev, Error
> **errp)
> dev->conf.rerror = BLOCKDEV_ON_ERROR_AUTO;
> dev->conf.werror = BLOCKDEV_ON_ERROR_AUTO;
>
> - if (!blkconf_apply_backend_options(&dev->conf,
> - blk_is_read_only(dev->conf.blk),
> - false, errp)) {
> + if (!blkconf_apply_backend_options(&dev->conf, read_only, false, errp)) {
> return;
> }
>
>
Smells correct.
Reviewed-by: John Snow <address@hidden>