From: David Gibson <david@gibson.dropbear.id.au>
To: "wangyanan (Y)" <wangyanan55@huawei.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
Andrew Jones <drjones@redhat.com>,
"Michael S . Tsirkin" <mst@redhat.com>,
wanghaibin.wang@huawei.com, qemu-devel@nongnu.org,
Shannon Zhao <shannon.zhaosl@gmail.com>,
qemu-arm@nongnu.org, Alistair Francis <alistair.francis@wdc.com>,
prime.zeng@hisilicon.com, yangyicong@huawei.com,
yuzenghui@huawei.com, Igor Mammedov <imammedo@redhat.com>,
zhukeqian1@huawei.com, Jiajie Li <lijiajie11@huawei.com>
Subject: Re: [RFC PATCH v2 1/6] device_tree: Add qemu_fdt_add_path
Date: Mon, 19 Apr 2021 11:13:10 +1000 [thread overview]
Message-ID: <YHzZJvH/9CiYWia4@yekko.fritz.box> (raw)
In-Reply-To: <cd3408c2-6025-7a44-bbf6-d675467c5749@huawei.com>
[-- Attachment #1: Type: text/plain, Size: 6091 bytes --]
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.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2021-04-19 3:10 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 8:07 [RFC PATCH v2 0/6] hw/arm/virt: Introduce cpu topology support Yanan Wang
2021-04-13 8:07 ` [RFC PATCH v2 1/6] device_tree: Add qemu_fdt_add_path Yanan Wang
2021-04-16 4:52 ` David Gibson
2021-04-17 2:36 ` wangyanan (Y)
2021-04-19 1:13 ` David Gibson [this message]
2021-04-19 7:02 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 2/6] hw/arm/virt: DT: Add cpu-map Yanan Wang
2021-04-27 9:47 ` Philippe Mathieu-Daudé
2021-04-27 10:04 ` Andrew Jones
2021-04-27 12:36 ` Philippe Mathieu-Daudé
2021-04-28 6:36 ` wangyanan (Y)
2021-05-13 6:58 ` Andrew Jones
2021-05-13 7:15 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 3/6] hw/arm/virt-acpi-build: Distinguish possible and present cpus Yanan Wang
2021-04-27 13:18 ` Andrew Jones
2021-04-28 6:42 ` wangyanan (Y)
2021-04-27 14:50 ` Andrew Jones
2021-04-28 6:47 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 4/6] hw/acpi/aml-build: Add processor hierarchy node structure Yanan Wang
2021-04-27 13:37 ` Andrew Jones
2021-04-28 6:59 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table Yanan Wang
2021-04-27 14:16 ` Andrew Jones
2021-04-28 7:30 ` wangyanan (Y)
2021-05-13 5:10 ` wangyanan (Y)
2021-05-13 6:55 ` Andrew Jones
2021-05-18 7:17 ` Salil Mehta
2021-05-18 7:42 ` Andrew Jones
2021-05-18 18:34 ` Salil Mehta
2021-05-18 19:05 ` Andrew Jones
2021-05-18 19:22 ` Salil Mehta
2021-05-19 3:18 ` wangyanan (Y)
2021-05-19 7:54 ` Salil Mehta
2021-05-19 8:15 ` Andrew Jones
2021-05-19 8:42 ` wangyanan (Y)
2021-05-19 10:00 ` Salil Mehta
2021-05-19 8:27 ` Andrew Jones
2021-05-19 13:26 ` wangyanan (Y)
2021-05-19 13:40 ` wangyanan (Y)
2021-05-18 9:16 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 6/6] hw/arm/virt: Replace smp_parse with one that prefers cores Yanan Wang
2021-04-27 14:58 ` Andrew Jones
2021-04-28 8:04 ` wangyanan (Y)
2021-04-28 9:36 ` wangyanan (Y)
2021-04-28 10:13 ` Andrew Jones
2021-04-29 2:21 ` wangyanan (Y)
2021-04-21 7:40 ` [RFC PATCH v2 0/6] hw/arm/virt: Introduce cpu topology support wangyanan (Y)
2021-04-21 9:31 ` wangyanan (Y)
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