diff mbox series

[RFC,v2,1/6] device_tree: Add qemu_fdt_add_path

Message ID 20210413080745.33004-2-wangyanan55@huawei.com (mailing list archive)
State New
Headers show
Series hw/arm/virt: Introduce cpu topology support | expand

Commit Message

wangyanan (Y) April 13, 2021, 8:07 a.m. UTC
From: Andrew Jones <drjones@redhat.com>

qemu_fdt_add_path() works like qemu_fdt_add_subnode(), except
it also adds any missing subnodes in the path. We also tweak
an error message of qemu_fdt_add_subnode().

We'll make use of this new function in a coming patch.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
---
 include/sysemu/device_tree.h |  1 +
 softmmu/device_tree.c        | 45 ++++++++++++++++++++++++++++++++++--
 2 files changed, 44 insertions(+), 2 deletions(-)

Comments

David Gibson April 16, 2021, 4:52 a.m. UTC | #1
On Tue, Apr 13, 2021 at 04:07:40PM +0800, Yanan Wang wrote:
> From: Andrew Jones <drjones@redhat.com>
> 
> qemu_fdt_add_path() works like qemu_fdt_add_subnode(), except
> it also adds any missing subnodes in the path. We also tweak
> an error message of qemu_fdt_add_subnode().
> 
> We'll make use of this new function in a coming patch.
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> ---
>  include/sysemu/device_tree.h |  1 +
>  softmmu/device_tree.c        | 45 ++++++++++++++++++++++++++++++++++--
>  2 files changed, 44 insertions(+), 2 deletions(-)
> 
> diff --git a/include/sysemu/device_tree.h b/include/sysemu/device_tree.h
> index 8a2fe55622..ef060a9759 100644
> --- a/include/sysemu/device_tree.h
> +++ b/include/sysemu/device_tree.h
> @@ -121,6 +121,7 @@ uint32_t qemu_fdt_get_phandle(void *fdt, const char *path);
>  uint32_t qemu_fdt_alloc_phandle(void *fdt);
>  int qemu_fdt_nop_node(void *fdt, const char *node_path);
>  int qemu_fdt_add_subnode(void *fdt, const char *name);
> +int qemu_fdt_add_path(void *fdt, const char *path);
>  
>  #define qemu_fdt_setprop_cells(fdt, node_path, property, ...)                 \
>      do {                                                                      \
> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> index 2691c58cf6..8592c7aa1b 100644
> --- a/softmmu/device_tree.c
> +++ b/softmmu/device_tree.c
> @@ -541,8 +541,8 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
>  
>      retval = fdt_add_subnode(fdt, parent, basename);
>      if (retval < 0) {
> -        error_report("FDT: Failed to create subnode %s: %s", name,
> -                     fdt_strerror(retval));
> +        error_report("%s: Failed to create subnode %s: %s",
> +                     __func__, name, fdt_strerror(retval));
>          exit(1);
>      }
>  
> @@ -550,6 +550,47 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
>      return retval;
>  }
>  
> +/*
> + * Like qemu_fdt_add_subnode(), but will add all missing
> + * subnodes in the path.
> + */
> +int qemu_fdt_add_path(void *fdt, const char *path)
> +{
> +    char *dupname, *basename, *p;
> +    int parent, retval = -1;
> +
> +    if (path[0] != '/') {
> +        return retval;
> +    }
> +
> +    parent = fdt_path_offset(fdt, "/");

Getting the offset for "/" is never needed - it's always 0.

> +    p = dupname = g_strdup(path);

You shouldn't need the strdup(), see below.

> +
> +    while (p) {
> +        *p = '/';
> +        basename = p + 1;
> +        p = strchr(p + 1, '/');
> +        if (p) {
> +            *p = '\0';
> +        }
> +        retval = fdt_path_offset(fdt, dupname);

The fdt_path_offset_namelen() function exists *exactly* so that you
can look up partial parths without having to mangle your input
string.  Just set the namelen right, and it will ignore anything to
the right of that.

> +        if (retval < 0 && retval != -FDT_ERR_NOTFOUND) {
> +            error_report("%s: Invalid path %s: %s",
> +                         __func__, path, fdt_strerror(retval));

If you're getting an error other than FDT_ERR_NOTFOUND here, chances
are it's not an invalid path, but a corrupted fdt blob or something
else.

> +            exit(1);
> +        } else if (retval == -FDT_ERR_NOTFOUND) {
> +            retval = fdt_add_subnode(fdt, parent, basename);
> +            if (retval < 0) {
> +                break;
> +            }
> +        }
> +        parent = retval;
> +    }
> +
> +    g_free(dupname);
> +    return retval;
> +}
> +
>  void qemu_fdt_dumpdtb(void *fdt, int size)
>  {
>      const char *dumpdtb = current_machine->dumpdtb;
wangyanan (Y) April 17, 2021, 2:36 a.m. UTC | #2
Hi David,

On 2021/4/16 12:52, David Gibson wrote:
> On Tue, Apr 13, 2021 at 04:07:40PM +0800, Yanan Wang wrote:
>> From: Andrew Jones <drjones@redhat.com>
>>
>> qemu_fdt_add_path() works like qemu_fdt_add_subnode(), except
>> it also adds any missing subnodes in the path. We also tweak
>> an error message of qemu_fdt_add_subnode().
>>
>> We'll make use of this new function in a coming patch.
>>
>> Signed-off-by: Andrew Jones <drjones@redhat.com>
>> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
>> ---
>>   include/sysemu/device_tree.h |  1 +
>>   softmmu/device_tree.c        | 45 ++++++++++++++++++++++++++++++++++--
>>   2 files changed, 44 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/sysemu/device_tree.h b/include/sysemu/device_tree.h
>> index 8a2fe55622..ef060a9759 100644
>> --- a/include/sysemu/device_tree.h
>> +++ b/include/sysemu/device_tree.h
>> @@ -121,6 +121,7 @@ uint32_t qemu_fdt_get_phandle(void *fdt, const char *path);
>>   uint32_t qemu_fdt_alloc_phandle(void *fdt);
>>   int qemu_fdt_nop_node(void *fdt, const char *node_path);
>>   int qemu_fdt_add_subnode(void *fdt, const char *name);
>> +int qemu_fdt_add_path(void *fdt, const char *path);
>>   
>>   #define qemu_fdt_setprop_cells(fdt, node_path, property, ...)                 \
>>       do {                                                                      \
>> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
>> index 2691c58cf6..8592c7aa1b 100644
>> --- a/softmmu/device_tree.c
>> +++ b/softmmu/device_tree.c
>> @@ -541,8 +541,8 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
>>   
>>       retval = fdt_add_subnode(fdt, parent, basename);
>>       if (retval < 0) {
>> -        error_report("FDT: Failed to create subnode %s: %s", name,
>> -                     fdt_strerror(retval));
>> +        error_report("%s: Failed to create subnode %s: %s",
>> +                     __func__, name, fdt_strerror(retval));
>>           exit(1);
>>       }
>>   
>> @@ -550,6 +550,47 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
>>       return retval;
>>   }
>>   
>> +/*
>> + * Like qemu_fdt_add_subnode(), but will add all missing
>> + * subnodes in the path.
>> + */
>> +int qemu_fdt_add_path(void *fdt, const char *path)
>> +{
>> +    char *dupname, *basename, *p;
>> +    int parent, retval = -1;
>> +
>> +    if (path[0] != '/') {
>> +        return retval;
>> +    }
>> +
>> +    parent = fdt_path_offset(fdt, "/");
> Getting the offset for "/" is never needed - it's always 0.
Thanks, will fix it.
>> +    p = dupname = g_strdup(path);
> You shouldn't need the strdup(), see below.
>
>> +
>> +    while (p) {
>> +        *p = '/';
>> +        basename = p + 1;
>> +        p = strchr(p + 1, '/');
>> +        if (p) {
>> +            *p = '\0';
>> +        }
>> +        retval = fdt_path_offset(fdt, dupname);
> The fdt_path_offset_namelen() function exists *exactly* so that you
> can look up partial parths without having to mangle your input
> string.  Just set the namelen right, and it will ignore anything to
> the right of that.
Function fdt_path_offset_namelen() seems more reasonable.

After we call qemu_fdt_add_path() to add "/cpus/cpu-map/socket0/core0" 
successfully,
if we want to add another path like "/cpus/cpu-map/socket0/core1" we 
will get the error
-FDT_ERR_NOTFOUND for each partial path. But actually 
"/cpus/cpu-map/socket0"
already exists, so by using fdt_path_offset_namelen() with right namelen 
we can avoid
the error retval for this part.
>> +        if (retval < 0 && retval != -FDT_ERR_NOTFOUND) {
>> +            error_report("%s: Invalid path %s: %s",
>> +                         __func__, path, fdt_strerror(retval));
> If you're getting an error other than FDT_ERR_NOTFOUND here, chances
> are it's not an invalid path, but a corrupted fdt blob or something
> else.

Right, there can be variable reasons for the fail in addition to the 
invalid path.

>> +            exit(1);
>> +        } else if (retval == -FDT_ERR_NOTFOUND) {
>> +            retval = fdt_add_subnode(fdt, parent, basename);
>> +            if (retval < 0) {
>> +                break;
>> +            }
I found another question here. If path "/cpus/cpu-map/socket0/core0" has 
already
been added, when we want to add another path "/cpus/cpu-map/socket0/core1"
and go here with retval = fdt_add_subnode(fdt, parent, "cpus"), then 
retval will
be -FDT_ERR_EXISTS, but we can't just break the loop in this case.

Am I right of the explanation ?

Thanks,
Yanan
>> +        }
>> +        parent = retval;
>> +    }
>> +
>> +    g_free(dupname);
>> +    return retval;
>> +}
>> +
>>   void qemu_fdt_dumpdtb(void *fdt, int size)
>>   {
>>       const char *dumpdtb = current_machine->dumpdtb;
David Gibson April 19, 2021, 1:13 a.m. UTC | #3
On Sat, Apr 17, 2021 at 10:36:20AM +0800, wangyanan (Y) wrote:
> Hi David,
> 
> On 2021/4/16 12:52, David Gibson wrote:
> > On Tue, Apr 13, 2021 at 04:07:40PM +0800, Yanan Wang wrote:
> > > From: Andrew Jones <drjones@redhat.com>
> > > 
> > > qemu_fdt_add_path() works like qemu_fdt_add_subnode(), except
> > > it also adds any missing subnodes in the path. We also tweak
> > > an error message of qemu_fdt_add_subnode().
> > > 
> > > We'll make use of this new function in a coming patch.
> > > 
> > > Signed-off-by: Andrew Jones <drjones@redhat.com>
> > > Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> > > ---
> > >   include/sysemu/device_tree.h |  1 +
> > >   softmmu/device_tree.c        | 45 ++++++++++++++++++++++++++++++++++--
> > >   2 files changed, 44 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/sysemu/device_tree.h b/include/sysemu/device_tree.h
> > > index 8a2fe55622..ef060a9759 100644
> > > --- a/include/sysemu/device_tree.h
> > > +++ b/include/sysemu/device_tree.h
> > > @@ -121,6 +121,7 @@ uint32_t qemu_fdt_get_phandle(void *fdt, const char *path);
> > >   uint32_t qemu_fdt_alloc_phandle(void *fdt);
> > >   int qemu_fdt_nop_node(void *fdt, const char *node_path);
> > >   int qemu_fdt_add_subnode(void *fdt, const char *name);
> > > +int qemu_fdt_add_path(void *fdt, const char *path);
> > >   #define qemu_fdt_setprop_cells(fdt, node_path, property, ...)                 \
> > >       do {                                                                      \
> > > diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> > > index 2691c58cf6..8592c7aa1b 100644
> > > --- a/softmmu/device_tree.c
> > > +++ b/softmmu/device_tree.c
> > > @@ -541,8 +541,8 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
> > >       retval = fdt_add_subnode(fdt, parent, basename);
> > >       if (retval < 0) {
> > > -        error_report("FDT: Failed to create subnode %s: %s", name,
> > > -                     fdt_strerror(retval));
> > > +        error_report("%s: Failed to create subnode %s: %s",
> > > +                     __func__, name, fdt_strerror(retval));
> > >           exit(1);
> > >       }
> > > @@ -550,6 +550,47 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
> > >       return retval;
> > >   }
> > > +/*
> > > + * Like qemu_fdt_add_subnode(), but will add all missing
> > > + * subnodes in the path.
> > > + */
> > > +int qemu_fdt_add_path(void *fdt, const char *path)
> > > +{
> > > +    char *dupname, *basename, *p;
> > > +    int parent, retval = -1;
> > > +
> > > +    if (path[0] != '/') {
> > > +        return retval;
> > > +    }
> > > +
> > > +    parent = fdt_path_offset(fdt, "/");
> > Getting the offset for "/" is never needed - it's always 0.
> Thanks, will fix it.
> > > +    p = dupname = g_strdup(path);
> > You shouldn't need the strdup(), see below.
> > 
> > > +
> > > +    while (p) {
> > > +        *p = '/';
> > > +        basename = p + 1;
> > > +        p = strchr(p + 1, '/');
> > > +        if (p) {
> > > +            *p = '\0';
> > > +        }
> > > +        retval = fdt_path_offset(fdt, dupname);
> > The fdt_path_offset_namelen() function exists *exactly* so that you
> > can look up partial parths without having to mangle your input
> > string.  Just set the namelen right, and it will ignore anything to
> > the right of that.
> Function fdt_path_offset_namelen() seems more reasonable.
> 
> After we call qemu_fdt_add_path() to add "/cpus/cpu-map/socket0/core0"
> successfully,
> if we want to add another path like "/cpus/cpu-map/socket0/core1" we will
> get the error
> -FDT_ERR_NOTFOUND for each partial path. But actually
> "/cpus/cpu-map/socket0"
> already exists, so by using fdt_path_offset_namelen() with right namelen we
> can avoid
> the error retval for this part.

I don't quite follow what you're saying here.  AFAICT your logic was
correct - it just involved a lot of mangling the given path (adding
and removing \0s) which becomes unnecessary with
fdt_path_offset_namelen().

> > > +        if (retval < 0 && retval != -FDT_ERR_NOTFOUND) {
> > > +            error_report("%s: Invalid path %s: %s",
> > > +                         __func__, path, fdt_strerror(retval));
> > If you're getting an error other than FDT_ERR_NOTFOUND here, chances
> > are it's not an invalid path, but a corrupted fdt blob or something
> > else.
> 
> Right, there can be variable reasons for the fail in addition to the invalid
> path.
> 
> > > +            exit(1);
> > > +        } else if (retval == -FDT_ERR_NOTFOUND) {
> > > +            retval = fdt_add_subnode(fdt, parent, basename);
> > > +            if (retval < 0) {
> > > +                break;
> > > +            }
> I found another question here. If path "/cpus/cpu-map/socket0/core0" has
> already
> been added, when we want to add another path "/cpus/cpu-map/socket0/core1"
> and go here with retval = fdt_add_subnode(fdt, parent, "cpus"), then retval
> will
> be -FDT_ERR_EXISTS, but we can't just break the loop in this case.
> 
> Am I right of the explanation ?

Not exactly.  If you called that fdt_add_subnode() in that case you
would get FDT_ERR_EXISTS.  However, because the previous
fdt_path_offset() has returned -FDT_ERR_NOTFOUND, you've already
established that the partial path doesn't exist, so if you got an
FDT_ERR_EXISTS here something has gone very strangely wrong (such as
concurrent access to the flat tree, which would very likely corrupt
it).

Note that the repeated use of fdt_path_offset() in this function will
repeatedly rescan the whole fdt from the beginning.  If you're
concerned about performance (which you might well not be), then a more
efficient approach would be to take your input path component by
component and use fdt_subnode_offset() directly.
wangyanan (Y) April 19, 2021, 7:02 a.m. UTC | #4
Hi David,

On 2021/4/19 9:13, David Gibson wrote:
> On Sat, Apr 17, 2021 at 10:36:20AM +0800, wangyanan (Y) wrote:
>> Hi David,
>>
>> On 2021/4/16 12:52, David Gibson wrote:
>>> On Tue, Apr 13, 2021 at 04:07:40PM +0800, Yanan Wang wrote:
>>>> From: Andrew Jones <drjones@redhat.com>
>>>>
>>>> qemu_fdt_add_path() works like qemu_fdt_add_subnode(), except
>>>> it also adds any missing subnodes in the path. We also tweak
>>>> an error message of qemu_fdt_add_subnode().
>>>>
>>>> We'll make use of this new function in a coming patch.
>>>>
>>>> Signed-off-by: Andrew Jones <drjones@redhat.com>
>>>> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
>>>> ---
>>>>    include/sysemu/device_tree.h |  1 +
>>>>    softmmu/device_tree.c        | 45 ++++++++++++++++++++++++++++++++++--
>>>>    2 files changed, 44 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/include/sysemu/device_tree.h b/include/sysemu/device_tree.h
>>>> index 8a2fe55622..ef060a9759 100644
>>>> --- a/include/sysemu/device_tree.h
>>>> +++ b/include/sysemu/device_tree.h
>>>> @@ -121,6 +121,7 @@ uint32_t qemu_fdt_get_phandle(void *fdt, const char *path);
>>>>    uint32_t qemu_fdt_alloc_phandle(void *fdt);
>>>>    int qemu_fdt_nop_node(void *fdt, const char *node_path);
>>>>    int qemu_fdt_add_subnode(void *fdt, const char *name);
>>>> +int qemu_fdt_add_path(void *fdt, const char *path);
>>>>    #define qemu_fdt_setprop_cells(fdt, node_path, property, ...)                 \
>>>>        do {                                                                      \
>>>> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
>>>> index 2691c58cf6..8592c7aa1b 100644
>>>> --- a/softmmu/device_tree.c
>>>> +++ b/softmmu/device_tree.c
>>>> @@ -541,8 +541,8 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
>>>>        retval = fdt_add_subnode(fdt, parent, basename);
>>>>        if (retval < 0) {
>>>> -        error_report("FDT: Failed to create subnode %s: %s", name,
>>>> -                     fdt_strerror(retval));
>>>> +        error_report("%s: Failed to create subnode %s: %s",
>>>> +                     __func__, name, fdt_strerror(retval));
>>>>            exit(1);
>>>>        }
>>>> @@ -550,6 +550,47 @@ int qemu_fdt_add_subnode(void *fdt, const char *name)
>>>>        return retval;
>>>>    }
>>>> +/*
>>>> + * Like qemu_fdt_add_subnode(), but will add all missing
>>>> + * subnodes in the path.
>>>> + */
>>>> +int qemu_fdt_add_path(void *fdt, const char *path)
>>>> +{
>>>> +    char *dupname, *basename, *p;
>>>> +    int parent, retval = -1;
>>>> +
>>>> +    if (path[0] != '/') {
>>>> +        return retval;
>>>> +    }
>>>> +
>>>> +    parent = fdt_path_offset(fdt, "/");
>>> Getting the offset for "/" is never needed - it's always 0.
>> Thanks, will fix it.
>>>> +    p = dupname = g_strdup(path);
>>> You shouldn't need the strdup(), see below.
>>>
>>>> +
>>>> +    while (p) {
>>>> +        *p = '/';
>>>> +        basename = p + 1;
>>>> +        p = strchr(p + 1, '/');
>>>> +        if (p) {
>>>> +            *p = '\0';
>>>> +        }
>>>> +        retval = fdt_path_offset(fdt, dupname);
>>> The fdt_path_offset_namelen() function exists *exactly* so that you
>>> can look up partial parths without having to mangle your input
>>> string.  Just set the namelen right, and it will ignore anything to
>>> the right of that.
>> Function fdt_path_offset_namelen() seems more reasonable.
>>
>> After we call qemu_fdt_add_path() to add "/cpus/cpu-map/socket0/core0"
>> successfully,
>> if we want to add another path like "/cpus/cpu-map/socket0/core1" we will
>> get the error
>> -FDT_ERR_NOTFOUND for each partial path. But actually
>> "/cpus/cpu-map/socket0"
>> already exists, so by using fdt_path_offset_namelen() with right namelen we
>> can avoid
>> the error retval for this part.
> I don't quite follow what you're saying here.  AFAICT your logic was
> correct - it just involved a lot of mangling the given path (adding
> and removing \0s) which becomes unnecessary with
> fdt_path_offset_namelen().
Right.
>>>> +        if (retval < 0 && retval != -FDT_ERR_NOTFOUND) {
>>>> +            error_report("%s: Invalid path %s: %s",
>>>> +                         __func__, path, fdt_strerror(retval));
>>> If you're getting an error other than FDT_ERR_NOTFOUND here, chances
>>> are it's not an invalid path, but a corrupted fdt blob or something
>>> else.
>> Right, there can be variable reasons for the fail in addition to the invalid
>> path.
>>
>>>> +            exit(1);
>>>> +        } else if (retval == -FDT_ERR_NOTFOUND) {
>>>> +            retval = fdt_add_subnode(fdt, parent, basename);
>>>> +            if (retval < 0) {
>>>> +                break;
>>>> +            }
>> I found another question here. If path "/cpus/cpu-map/socket0/core0" has
>> already
>> been added, when we want to add another path "/cpus/cpu-map/socket0/core1"
>> and go here with retval = fdt_add_subnode(fdt, parent, "cpus"), then retval
>> will
>> be -FDT_ERR_EXISTS, but we can't just break the loop in this case.
>>
>> Am I right of the explanation ?
> Not exactly.  If you called that fdt_add_subnode() in that case you
> would get FDT_ERR_EXISTS.  However, because the previous
> fdt_path_offset() has returned -FDT_ERR_NOTFOUND, you've already
> established that the partial path doesn't exist, so if you got an
> FDT_ERR_EXISTS here something has gone very strangely wrong (such as
> concurrent access to the flat tree, which would very likely corrupt
> it).
Thanks for the analysis, I was wrong...
> Note that the repeated use of fdt_path_offset() in this function will
> repeatedly rescan the whole fdt from the beginning.  If you're
> concerned about performance (which you might well not be), then a more
> efficient approach would be to take your input path component by
> component and use fdt_subnode_offset() directly.
I will try to address your comments and have some rework for this patch 
in next version.

Thanks,
Yanan
>
diff mbox series

Patch

diff --git a/include/sysemu/device_tree.h b/include/sysemu/device_tree.h
index 8a2fe55622..ef060a9759 100644
--- a/include/sysemu/device_tree.h
+++ b/include/sysemu/device_tree.h
@@ -121,6 +121,7 @@  uint32_t qemu_fdt_get_phandle(void *fdt, const char *path);
 uint32_t qemu_fdt_alloc_phandle(void *fdt);
 int qemu_fdt_nop_node(void *fdt, const char *node_path);
 int qemu_fdt_add_subnode(void *fdt, const char *name);
+int qemu_fdt_add_path(void *fdt, const char *path);
 
 #define qemu_fdt_setprop_cells(fdt, node_path, property, ...)                 \
     do {                                                                      \
diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
index 2691c58cf6..8592c7aa1b 100644
--- a/softmmu/device_tree.c
+++ b/softmmu/device_tree.c
@@ -541,8 +541,8 @@  int qemu_fdt_add_subnode(void *fdt, const char *name)
 
     retval = fdt_add_subnode(fdt, parent, basename);
     if (retval < 0) {
-        error_report("FDT: Failed to create subnode %s: %s", name,
-                     fdt_strerror(retval));
+        error_report("%s: Failed to create subnode %s: %s",
+                     __func__, name, fdt_strerror(retval));
         exit(1);
     }
 
@@ -550,6 +550,47 @@  int qemu_fdt_add_subnode(void *fdt, const char *name)
     return retval;
 }
 
+/*
+ * Like qemu_fdt_add_subnode(), but will add all missing
+ * subnodes in the path.
+ */
+int qemu_fdt_add_path(void *fdt, const char *path)
+{
+    char *dupname, *basename, *p;
+    int parent, retval = -1;
+
+    if (path[0] != '/') {
+        return retval;
+    }
+
+    parent = fdt_path_offset(fdt, "/");
+    p = dupname = g_strdup(path);
+
+    while (p) {
+        *p = '/';
+        basename = p + 1;
+        p = strchr(p + 1, '/');
+        if (p) {
+            *p = '\0';
+        }
+        retval = fdt_path_offset(fdt, dupname);
+        if (retval < 0 && retval != -FDT_ERR_NOTFOUND) {
+            error_report("%s: Invalid path %s: %s",
+                         __func__, path, fdt_strerror(retval));
+            exit(1);
+        } else if (retval == -FDT_ERR_NOTFOUND) {
+            retval = fdt_add_subnode(fdt, parent, basename);
+            if (retval < 0) {
+                break;
+            }
+        }
+        parent = retval;
+    }
+
+    g_free(dupname);
+    return retval;
+}
+
 void qemu_fdt_dumpdtb(void *fdt, int size)
 {
     const char *dumpdtb = current_machine->dumpdtb;