Add option to preserve owner when creating an entry in Xen Store. This
may be needed in cases when Qemu is working as device model in a
domain that is Domain-0, e.g. in driver domain.
"owner" parameter for qemu_xen_xs_create() function can have special
value XS_PRESERVE_OWNER, which will make specific implementation to
get original owner of an entry and pass it back to
set_permissions() call.
Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
---
hw/i386/kvm/xen_xenstore.c | 18 ++++++++++++++++++
hw/xen/xen-operations.c | 12 ++++++++++++
include/hw/xen/xen_backend_ops.h | 2 ++
3 files changed, 32 insertions(+)
diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
index 660d0b72f9..7b894a9884 100644
--- a/hw/i386/kvm/xen_xenstore.c
+++ b/hw/i386/kvm/xen_xenstore.c
@@ -1572,6 +1572,24 @@ static bool xs_be_create(struct qemu_xs_handle *h, xs_transaction_t t,
return false;
}
+ if (owner == XS_PRESERVE_OWNER) {
+ GList *perms;
+ char letter;
+
+ err = xs_impl_get_perms(h->impl, 0, t, path, &perms);
+ if (err) {
+ errno = err;
+ return false;
+ }
+
+ if (sscanf(perms->data, "%c%u", &letter, &owner) != 2) {
+ errno = EFAULT;
+ g_list_free_full(perms, g_free);
+ return false;
+ }
+ g_list_free_full(perms, g_free);
+ }
+
perms_list = g_list_append(perms_list,
xs_perm_as_string(XS_PERM_NONE, owner));
perms_list = g_list_append(perms_list,
diff --git a/hw/xen/xen-operations.c b/hw/xen/xen-operations.c
index e00983ec44..1df59b3c08 100644
--- a/hw/xen/xen-operations.c
+++ b/hw/xen/xen-operations.c
@@ -300,6 +300,18 @@ static bool libxenstore_create(struct qemu_xs_handle *h, xs_transaction_t t,
return false;
}
+ if (owner == XS_PRESERVE_OWNER) {
+ struct xs_permissions *tmp;
+ unsigned int num;
+
+ tmp = xs_get_permissions(h->xsh, 0, path, &num);
+ if (tmp == NULL) {
+ return false;
+ }
+ perms_list[0].id = tmp[0].id;
+ free(tmp);
+ }
+
return xs_set_permissions(h->xsh, t, path, perms_list,
ARRAY_SIZE(perms_list));
}
diff --git a/include/hw/xen/xen_backend_ops.h b/include/hw/xen/xen_backend_ops.h
index 90cca85f52..273e414559 100644
--- a/include/hw/xen/xen_backend_ops.h
+++ b/include/hw/xen/xen_backend_ops.h
@@ -266,6 +266,8 @@ typedef uint32_t xs_transaction_t;
#define XS_PERM_READ 0x01
#define XS_PERM_WRITE 0x02
+#define XS_PRESERVE_OWNER 0xFFFE
+
struct xenstore_backend_ops {
struct qemu_xs_handle *(*open)(void);
void (*close)(struct qemu_xs_handle *h);
--
2.42.0On 10/11/2023 15:42, Volodymyr Babchuk wrote:
> Add option to preserve owner when creating an entry in Xen Store. This
> may be needed in cases when Qemu is working as device model in a
> domain that is Domain-0, e.g. in driver domain.
>
> "owner" parameter for qemu_xen_xs_create() function can have special
> value XS_PRESERVE_OWNER, which will make specific implementation to
> get original owner of an entry and pass it back to
> set_permissions() call.
>
If QEMU is running in a driver domain then it should know whether the
domid of the domain it is running in and use that. Yes, it is hardcoded
to 0 at the moment but surely a backend domid (which defaults to 0)
could be passed on the command line?
Paul
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
> ---
> hw/i386/kvm/xen_xenstore.c | 18 ++++++++++++++++++
> hw/xen/xen-operations.c | 12 ++++++++++++
> include/hw/xen/xen_backend_ops.h | 2 ++
> 3 files changed, 32 insertions(+)
>
> diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
> index 660d0b72f9..7b894a9884 100644
> --- a/hw/i386/kvm/xen_xenstore.c
> +++ b/hw/i386/kvm/xen_xenstore.c
> @@ -1572,6 +1572,24 @@ static bool xs_be_create(struct qemu_xs_handle *h, xs_transaction_t t,
> return false;
> }
>
> + if (owner == XS_PRESERVE_OWNER) {
> + GList *perms;
> + char letter;
> +
> + err = xs_impl_get_perms(h->impl, 0, t, path, &perms);
> + if (err) {
> + errno = err;
> + return false;
> + }
> +
> + if (sscanf(perms->data, "%c%u", &letter, &owner) != 2) {
> + errno = EFAULT;
> + g_list_free_full(perms, g_free);
> + return false;
> + }
> + g_list_free_full(perms, g_free);
> + }
> +
> perms_list = g_list_append(perms_list,
> xs_perm_as_string(XS_PERM_NONE, owner));
> perms_list = g_list_append(perms_list,
> diff --git a/hw/xen/xen-operations.c b/hw/xen/xen-operations.c
> index e00983ec44..1df59b3c08 100644
> --- a/hw/xen/xen-operations.c
> +++ b/hw/xen/xen-operations.c
> @@ -300,6 +300,18 @@ static bool libxenstore_create(struct qemu_xs_handle *h, xs_transaction_t t,
> return false;
> }
>
> + if (owner == XS_PRESERVE_OWNER) {
> + struct xs_permissions *tmp;
> + unsigned int num;
> +
> + tmp = xs_get_permissions(h->xsh, 0, path, &num);
> + if (tmp == NULL) {
> + return false;
> + }
> + perms_list[0].id = tmp[0].id;
> + free(tmp);
> + }
> +
> return xs_set_permissions(h->xsh, t, path, perms_list,
> ARRAY_SIZE(perms_list));
> }
> diff --git a/include/hw/xen/xen_backend_ops.h b/include/hw/xen/xen_backend_ops.h
> index 90cca85f52..273e414559 100644
> --- a/include/hw/xen/xen_backend_ops.h
> +++ b/include/hw/xen/xen_backend_ops.h
> @@ -266,6 +266,8 @@ typedef uint32_t xs_transaction_t;
> #define XS_PERM_READ 0x01
> #define XS_PERM_WRITE 0x02
>
> +#define XS_PRESERVE_OWNER 0xFFFE
> +
> struct xenstore_backend_ops {
> struct qemu_xs_handle *(*open)(void);
> void (*close)(struct qemu_xs_handle *h);
On Fri, 2023-11-10 at 20:42 +0000, Volodymyr Babchuk wrote:
> Add option to preserve owner when creating an entry in Xen Store. This
> may be needed in cases when Qemu is working as device model in a
> domain that is Domain-0, e.g. in driver domain.
>
> "owner" parameter for qemu_xen_xs_create() function can have special
> value XS_PRESERVE_OWNER, which will make specific implementation to
> get original owner of an entry and pass it back to
> set_permissions() call.
>
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
I like this, although I'd like it more if XenStore itself offered this
facility rather than making QEMU do it. Can we make it abundantly clear
that XS_PRESERVE_OWNER is a QEMU internal thing?
> hw/i386/kvm/xen_xenstore.c | 18 ++++++++++++++++++
> hw/xen/xen-operations.c | 12 ++++++++++++
> include/hw/xen/xen_backend_ops.h | 2 ++
> 3 files changed, 32 insertions(+)
>
> diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
> index 660d0b72f9..7b894a9884 100644
> --- a/hw/i386/kvm/xen_xenstore.c
> +++ b/hw/i386/kvm/xen_xenstore.c
> @@ -1572,6 +1572,24 @@ static bool xs_be_create(struct qemu_xs_handle *h, xs_transaction_t t,
> return false;
> }
>
> + if (owner == XS_PRESERVE_OWNER) {
> + GList *perms;
> + char letter;
> +
> + err = xs_impl_get_perms(h->impl, 0, t, path, &perms);
> + if (err) {
> + errno = err;
> + return false;
> + }
I guess we get away without a race here because it's all internal and
we're holding the QEMU iothread mutex? Perhaps assert that?
> + if (sscanf(perms->data, "%c%u", &letter, &owner) != 2) {
I'd be slightly happier if you used parse_perm() from xenstore_impl.c,
but it's static so I suppose that's fair enough.
> + errno = EFAULT;
> + g_list_free_full(perms, g_free);
> + return false;
> + }
> + g_list_free_full(perms, g_free);
> + }
> +
> perms_list = g_list_append(perms_list,
> xs_perm_as_string(XS_PERM_NONE, owner));
> perms_list = g_list_append(perms_list,
> diff --git a/hw/xen/xen-operations.c b/hw/xen/xen-operations.c
> index e00983ec44..1df59b3c08 100644
> --- a/hw/xen/xen-operations.c
> +++ b/hw/xen/xen-operations.c
> @@ -300,6 +300,18 @@ static bool libxenstore_create(struct qemu_xs_handle *h, xs_transaction_t t,
> return false;
> }
>
> + if (owner == XS_PRESERVE_OWNER) {
> + struct xs_permissions *tmp;
> + unsigned int num;
> +
> + tmp = xs_get_permissions(h->xsh, 0, path, &num);
> + if (tmp == NULL) {
> + return false;
> + }
> + perms_list[0].id = tmp[0].id;
> + free(tmp);
> + }
> +
Don't see what saves you from someone else changing it at this point on
true Xen though. Which is why I'd prefer XenStore to do it natively.
> return xs_set_permissions(h->xsh, t, path, perms_list,
> ARRAY_SIZE(perms_list));
> }
> diff --git a/include/hw/xen/xen_backend_ops.h b/include/hw/xen/xen_backend_ops.h
> index 90cca85f52..273e414559 100644
> --- a/include/hw/xen/xen_backend_ops.h
> +++ b/include/hw/xen/xen_backend_ops.h
> @@ -266,6 +266,8 @@ typedef uint32_t xs_transaction_t;
> #define XS_PERM_READ 0x01
> #define XS_PERM_WRITE 0x02
>
> +#define XS_PRESERVE_OWNER 0xFFFE
> +
> struct xenstore_backend_ops {
> struct qemu_xs_handle *(*open)(void);
> void (*close)(struct qemu_xs_handle *h);
Hi David,
David Woodhouse <dwmw2@infradead.org> writes:
> [[S/MIME Signed Part:Undecided]]
> On Fri, 2023-11-10 at 20:42 +0000, Volodymyr Babchuk wrote:
>> Add option to preserve owner when creating an entry in Xen Store. This
>> may be needed in cases when Qemu is working as device model in a
>> domain that is Domain-0, e.g. in driver domain.
>>
>> "owner" parameter for qemu_xen_xs_create() function can have special
>> value XS_PRESERVE_OWNER, which will make specific implementation to
>> get original owner of an entry and pass it back to
>> set_permissions() call.
>>
>> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
>
> I like this, although I'd like it more if XenStore itself offered this
> facility rather than making QEMU do it.
XenStore itself ensures that access rights are inherited. The problem
is with qemu_xen_xs_create() function that does two things at a time:
creates a new entry and then assigns permissions, overwriting any
permissions that existed before.
> Can we make it abundantly clear
> that XS_PRESERVE_OWNER is a QEMU internal thing?
It is defined in xen_backend_ops.h which is internal QEMU interface for
XenStore. Do you have any suggestions how to make it even clearer?
>> hw/i386/kvm/xen_xenstore.c | 18 ++++++++++++++++++
>> hw/xen/xen-operations.c | 12 ++++++++++++
>> include/hw/xen/xen_backend_ops.h | 2 ++
>> 3 files changed, 32 insertions(+)
>>
>> diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
>> index 660d0b72f9..7b894a9884 100644
>> --- a/hw/i386/kvm/xen_xenstore.c
>> +++ b/hw/i386/kvm/xen_xenstore.c
>> @@ -1572,6 +1572,24 @@ static bool xs_be_create(struct qemu_xs_handle *h, xs_transaction_t t,
>> return false;
>> }
>>
>> + if (owner == XS_PRESERVE_OWNER) {
>> + GList *perms;
>> + char letter;
>> +
>> + err = xs_impl_get_perms(h->impl, 0, t, path, &perms);
>> + if (err) {
>> + errno = err;
>> + return false;
>> + }
>
> I guess we get away without a race here because it's all internal and
> we're holding the QEMU iothread mutex? Perhaps assert that?
>
I am not quite familiar with QEMU internals, but why we do we need
assert here? xe_be_create() calls xs_impl* function before and after
this part. Is this piece of code special in some way?
>> + if (sscanf(perms->data, "%c%u", &letter, &owner) != 2) {
>
> I'd be slightly happier if you used parse_perm() from xenstore_impl.c,
> but it's static so I suppose that's fair enough.
>
Yes, I wanted to use that function, but it is internal for
xenstore_impl.c
I can rename it to xs_impl_parse_perm() and make it public, if you
believe that this is a better approach.
>> + errno = EFAULT;
>> + g_list_free_full(perms, g_free);
>> + return false;
>> + }
>> + g_list_free_full(perms, g_free);
>> + }
>> +
>> perms_list = g_list_append(perms_list,
>> xs_perm_as_string(XS_PERM_NONE, owner));
>> perms_list = g_list_append(perms_list,
>> diff --git a/hw/xen/xen-operations.c b/hw/xen/xen-operations.c
>> index e00983ec44..1df59b3c08 100644
>> --- a/hw/xen/xen-operations.c
>> +++ b/hw/xen/xen-operations.c
>> @@ -300,6 +300,18 @@ static bool libxenstore_create(struct qemu_xs_handle *h, xs_transaction_t t,
>> return false;
>> }
>>
>> + if (owner == XS_PRESERVE_OWNER) {
>> + struct xs_permissions *tmp;
>> + unsigned int num;
>> +
>> + tmp = xs_get_permissions(h->xsh, 0, path, &num);
>> + if (tmp == NULL) {
>> + return false;
>> + }
>> + perms_list[0].id = tmp[0].id;
>> + free(tmp);
>> + }
>> +
>
> Don't see what saves you from someone else changing it at this point on
> true Xen though. Which is why I'd prefer XenStore to do it natively.
>
Oh, I missed the transaction parameter. My bad. Will fix in the next
version.
>> return xs_set_permissions(h->xsh, t, path, perms_list,
>> ARRAY_SIZE(perms_list));
>> }
>> diff --git a/include/hw/xen/xen_backend_ops.h b/include/hw/xen/xen_backend_ops.h
>> index 90cca85f52..273e414559 100644
>> --- a/include/hw/xen/xen_backend_ops.h
>> +++ b/include/hw/xen/xen_backend_ops.h
>> @@ -266,6 +266,8 @@ typedef uint32_t xs_transaction_t;
>> #define XS_PERM_READ 0x01
>> #define XS_PERM_WRITE 0x02
>>
>> +#define XS_PRESERVE_OWNER 0xFFFE
>> +
>> struct xenstore_backend_ops {
>> struct qemu_xs_handle *(*open)(void);
>> void (*close)(struct qemu_xs_handle *h);
>
> [[End of S/MIME Signed Part]]
--
WBR, Volodymyr
On Sat, 2023-11-11 at 11:01 +0000, David Woodhouse wrote:
>
> > --- a/hw/xen/xen-operations.c
> > +++ b/hw/xen/xen-operations.c
> > @@ -300,6 +300,18 @@ static bool libxenstore_create(struct qemu_xs_handle *h, xs_transaction_t t,
> > return false;
> > }
> >
> > + if (owner == XS_PRESERVE_OWNER) {
> > + struct xs_permissions *tmp;
> > + unsigned int num;
> > +
> > + tmp = xs_get_permissions(h->xsh, 0, path, &num);
> > + if (tmp == NULL) {
> > + return false;
> > + }
> > + perms_list[0].id = tmp[0].id;
> > + free(tmp);
> > + }
> > +
>
> Don't see what saves you from someone else changing it at this point on
> true Xen though. Which is why I'd prefer XenStore to do it natively.
I suppose maybe you could do it in a transaction *if* the transaction_t
you're passed in isn't already XBT_NULL?
One might argue that the mkdir+set_perms in libxenstore_create() ought
to have been within the same transaction *anyway*?
Hi David,
David Woodhouse <dwmw2@infradead.org> writes:
> [[S/MIME Signed Part:Undecided]]
> On Sat, 2023-11-11 at 11:01 +0000, David Woodhouse wrote:
>>
>> > --- a/hw/xen/xen-operations.c
>> > +++ b/hw/xen/xen-operations.c
>> > @@ -300,6 +300,18 @@ static bool libxenstore_create(struct qemu_xs_handle *h, xs_transaction_t t,
>> > return false;
>> > }
>> >
>> > + if (owner == XS_PRESERVE_OWNER) {
>> > + struct xs_permissions *tmp;
>> > + unsigned int num;
>> > +
>> > + tmp = xs_get_permissions(h->xsh, 0, path, &num);
>> > + if (tmp == NULL) {
>> > + return false;
>> > + }
>> > + perms_list[0].id = tmp[0].id;
>> > + free(tmp);
>> > + }
>> > +
>>
>> Don't see what saves you from someone else changing it at this point on
>> true Xen though. Which is why I'd prefer XenStore to do it natively.
>
> I suppose maybe you could do it in a transaction *if* the transaction_t
> you're passed in isn't already XBT_NULL?
Yes, I need to pass "t" to xs_get_permissions(), of course.
> One might argue that the mkdir+set_perms in libxenstore_create() ought
> to have been within the same transaction *anyway*?
Yes, all operations should be performed inside one transaction.
--
WBR, Volodymyr
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