Re: [Qemu-devel] [v1 Patch 5/10]Qemu: raw-posix image file reopen

[Eric Blake <eblake@redhat.com>]

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On 06/15/2012 02:48 PM, Supriya Kannery wrote:
> raw-posix driver changes for bdrv_reopen_xx functions to
> safely reopen image files. Reopening of image files while 
> changing hostcache dynamically is handled here.
> 
> Signed-off-by: Supriya Kannery <supriyak@linux.vnet.ibm.com>
> 

>  
> +static int raw_reopen_prepare(BlockDriverState *bs, BDRVReopenState **prs,
> +                              int flags)
> +{
> +    BDRVRawReopenState *raw_rs = g_malloc0(sizeof(BDRVRawReopenState));
> +    BDRVRawState *s = bs->opaque;
> +    int ret = 0;
> +
> +    raw_rs->reopen_state.bs = bs;
> +
> +    /* stash state before reopen */
> +    raw_rs->stash_s = g_malloc0(sizeof(BDRVRawState));
> +/*    memcpy(raw_rs->stash_s, s, sizeof(BDRVRawState)); */

Why the comment?

> +    raw_stash_state(raw_rs->stash_s, s);
> +    s->fd = dup(raw_rs->stash_s->fd);

Needs to handle O_CLOEXEC open flag, which means using
fcntl(F_DUPFD_CLOEXEC) when available for atomic support, and a fallback
to fcntl(F_GETFD/F_SETFD) if not.

> +
> +    *prs = &(raw_rs->reopen_state);
> +
> +    /* Flags that can be set using fcntl */
> +    int fcntl_flags = BDRV_O_NOCACHE;
> +
> +    if ((bs->open_flags & ~fcntl_flags) == (flags & ~fcntl_flags)) {
> +        if ((flags & BDRV_O_NOCACHE)) {
> +            s->open_flags |= O_DIRECT;
> +        } else {
> +            s->open_flags &= ~O_DIRECT;
> +        }
> +        ret = fcntl_setfl(s->fd, s->open_flags);
> +    } else {
> +
> +        /* close and reopen using new flags */
> +        bs->drv->bdrv_close(bs);
> +        ret = bs->drv->bdrv_file_open(bs, bs->filename, flags);

Is this a case where Paolo's proposed bdrv_swap command would be useful?

> +    /* revert to stashed state */
> +    if (s->fd != -1) {
> +        close(s->fd);
> +    }
> +/*   memcpy(s, raw_rs->stash_s, sizeof(BDRVRawState)); */

Why the comment?

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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