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Re: [libvirt] [PATCH 01/12] qemu: Add a hash table for the shared disks



On Tue, Dec 11, 2012 at 21:37:18 +0800, Osier Yang wrote:
> This introduces a hash table for qemu driver, to store the shared
> disk's info as (@disk_path, { ref_count, @orig_cdbfilter}). @ref_count
> is the number of domains which shares the disk. @orig_cdbfilter is
> the original cdbfilter setting of the shared disk, it will be used
> to restore the the disk's cdbfilter setting to original value by
> later patches.
> 
> * src/qemu/qemu_conf.h: (Add member 'sharedDisks' of type
>                          virHashTablePtr; New struct qemuSharedDiskEntry;
>                          Declare helpers qemuAddSharedDisk,
>                          qemuRemoveSharedDisk)
> * src/qemu/qemu_conf.c (Implement the two helpers)
> * src/qemu/qemu_process.c (Update 'sharedDisks' when domain
>                            starting and shutdown)
> * src/qemu/qemu_driver.c (Update 'sharedDisks' when attaching
>                           or detaching disk).
> 
> 0 is passed for orig_cdbfilter temporarily, later patches will update
> it.
> ---
>  src/qemu/qemu_conf.c    |   48 +++++++++++++++++++++++++++++++++++++++++++++++
>  src/qemu/qemu_conf.h    |   18 +++++++++++++++++
>  src/qemu/qemu_driver.c  |   17 ++++++++++++++++
>  src/qemu/qemu_process.c |   17 +++++++++++++++-
>  4 files changed, 99 insertions(+), 1 deletions(-)
> 
> diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
> index 8d380a1..2b21186 100644
> --- a/src/qemu/qemu_conf.c
> +++ b/src/qemu/qemu_conf.c
> @@ -556,3 +556,51 @@ qemuDriverCloseCallbackRunAll(virQEMUDriverPtr driver,
>  
>      virHashForEach(driver->closeCallbacks, qemuDriverCloseCallbackRun, &data);
>  }
> +
> +/* Increase ref count if the entry already exists, otherwise
> + * add a new entry.
> + */
> +int
> +qemuAddSharedDisk(virHashTablePtr sharedDisks,
> +                  const char *disk_path,
> +                  int orig_cdbfilter)
> +{
> +    qemuSharedDiskEntryPtr entry = NULL;
> +
> +    if ((entry = virHashLookup(sharedDisks, disk_path))) {
> +        entry->ref++;
> +    } else {
> +        if (VIR_ALLOC(entry) < 0)
> +            return -1;
> +
> +        entry->ref = 1;
> +        entry->orig_cdbfilter = orig_cdbfilter;
> +
> +        if (virHashAddEntry(sharedDisks, disk_path, entry))
> +            return -1;
> +    }

In addition to Daniel's comments, I think this hash table should contain
device number rather than disk path since /dev is full of symlinks. One
domain may be configured to use /dev/sdg while another one would use
/dev/disk/by-id/..., another one /dev/disk/by-uuid/... and they can all
lead to the same block device. Thus you need to canonicalize disk_path
first, e.g., into major:minor and store that in the hash table.

Jirka


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