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 > > > > > > 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 > > > Signed-off-by: Yanan Wang > > > --- > > > 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