[Qemu-devel] [PATCH] Remove O_NOATIME flag from 9pfs open() calls in readonly mode

[Qemu-devel] [PATCH] Remove O_NOATIME flag from 9pfs open() calls in readonly mode

[Daniel P. Berrange]

From: "Daniel P. Berrange" <berrange@redhat.com>

When 2c74c2cb4bedddbfa67628fbd5f9273b4e0e9903 added support for
the 'readonly' flag against 9p filesystems, it also made QEMU
add the O_NOATIME flag as a side-effect.

The O_NOATIME flag, however, may only be set by the file owner,
or a user with CAP_FOWNER capability.  QEMU cannot assume that
this is the case for filesytems exported to QEMU.

eg, run QEMU as non-root, and attempt to pass the host OS
filesystem through to the guest OS with readonly enable.
The result is that the guest OS cannot open any files at
all.

If O_NOATIME is really required, it should be optionally
enabled via a separate QEMU command line flag.

 * hw/9pfs/virtio-9p.c: Remove O_NOATIME

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 hw/9pfs/virtio-9p.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
index e6ba6ba..f8e2c07 100644
--- a/hw/9pfs/virtio-9p.c
+++ b/hw/9pfs/virtio-9p.c
@@ -1391,7 +1391,6 @@ static void v9fs_open(void *opaque)
                 err = -EROFS;
                 goto out;
             }
-            flags |= O_NOATIME;
         }
         err = v9fs_co_open(pdu, fidp, flags);
         if (err < 0) {
-- 
1.7.7.5

Re: [Qemu-devel] [PATCH] Remove O_NOATIME flag from 9pfs open() calls in readonly mode

[Daniel P. Berrange]

Any thoughts on this fix ?  Read-only mode is pretty useless without
it for non-root users.

Daniel

On Mon, Jan 16, 2012 at 06:11:40PM +0000, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange" <berrange@redhat.com>
> 
> When 2c74c2cb4bedddbfa67628fbd5f9273b4e0e9903 added support for
> the 'readonly' flag against 9p filesystems, it also made QEMU
> add the O_NOATIME flag as a side-effect.
> 
> The O_NOATIME flag, however, may only be set by the file owner,
> or a user with CAP_FOWNER capability.  QEMU cannot assume that
> this is the case for filesytems exported to QEMU.
> 
> eg, run QEMU as non-root, and attempt to pass the host OS
> filesystem through to the guest OS with readonly enable.
> The result is that the guest OS cannot open any files at
> all.
> 
> If O_NOATIME is really required, it should be optionally
> enabled via a separate QEMU command line flag.
> 
>  * hw/9pfs/virtio-9p.c: Remove O_NOATIME
> 
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  hw/9pfs/virtio-9p.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
> index e6ba6ba..f8e2c07 100644
> --- a/hw/9pfs/virtio-9p.c
> +++ b/hw/9pfs/virtio-9p.c
> @@ -1391,7 +1391,6 @@ static void v9fs_open(void *opaque)
>                  err = -EROFS;
>                  goto out;
>              }
> -            flags |= O_NOATIME;
>          }
>          err = v9fs_co_open(pdu, fidp, flags);
>          if (err < 0) {
> -- 
> 1.7.7.5
> 

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Re: [Qemu-devel] [PATCH] Remove O_NOATIME flag from 9pfs open() calls in readonly mode

[M. Mohan Kumar]

Acked-by: M. Mohan Kumar <mohan@in.ibm.com>

On Monday, January 16, 2012 11:41:40 PM Daniel P. Berrange wrote:
> From: "Daniel P. Berrange" <berrange@redhat.com>
> 
> When 2c74c2cb4bedddbfa67628fbd5f9273b4e0e9903 added support for
> the 'readonly' flag against 9p filesystems, it also made QEMU
> add the O_NOATIME flag as a side-effect.
> 
> The O_NOATIME flag, however, may only be set by the file owner,
> or a user with CAP_FOWNER capability.  QEMU cannot assume that
> this is the case for filesytems exported to QEMU.
> 
> eg, run QEMU as non-root, and attempt to pass the host OS
> filesystem through to the guest OS with readonly enable.
> The result is that the guest OS cannot open any files at
> all.
> 
> If O_NOATIME is really required, it should be optionally
> enabled via a separate QEMU command line flag.
> 
>  * hw/9pfs/virtio-9p.c: Remove O_NOATIME
> 
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  hw/9pfs/virtio-9p.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
> index e6ba6ba..f8e2c07 100644
> --- a/hw/9pfs/virtio-9p.c
> +++ b/hw/9pfs/virtio-9p.c
> @@ -1391,7 +1391,6 @@ static void v9fs_open(void *opaque)
>                  err = -EROFS;
>                  goto out;
>              }
> -            flags |= O_NOATIME;
>          }
>          err = v9fs_co_open(pdu, fidp, flags);
>          if (err < 0) {