Hi On Tue, Nov 24, 2015 at 4:37 PM, Anne Mulhern <amulh...@redhat.com> wrote: >> From: "David Herrmann" <dh.herrm...@gmail.com> >> On Tue, Nov 24, 2015 at 3:54 PM, Anne Mulhern <amulh...@redhat.com> wrote: >> >> From: "David Herrmann" <dh.herrm...@gmail.com> >> >> On Tue, Nov 17, 2015 at 11:57 PM, Anne Mulhern <amulh...@redhat.com> >> >> wrote: >> >> >> From: "David Herrmann" <dh.herrm...@gmail.com> >> >> >> On Mon, Nov 16, 2015 at 5:35 PM, Anne Mulhern <amulh...@redhat.com> >> >> >> wrote: >> >> >> > libudev has some cooperating procedures that return the keys for a >> >> >> > bunch >> >> >> > of >> >> >> > sysfs attributes for a given device. >> >> >> > >> >> >> > These attributes all correspond to files that are stored in the sysfs >> >> >> > device directory. >> >> >> > >> >> >> > In the same directory there are sometimes subdirectories, that >> >> >> > themselves >> >> >> > contain files >> >> >> > with information about their corresponding attribute. The dm >> >> >> > directory >> >> >> > is >> >> >> > one obvious >> >> >> > example. >> >> >> > >> >> >> > Are their any plans for libudev to add an ability to get the values >> >> >> > from >> >> >> > these subdirectories >> >> >> > as some kind of attributes? >> >> >> > >> >> >> > If no, why? >> >> >> >> >> >> sd_device_get_sysattr_value(device, "foo/bar/baz", &value); >> >> >> >> >> >> This should work fine (or its udev_device_* equivalent). >> >> >> >> >> >> Btw., I recommend just using readdir(), open(), read(), and write(). >> >> >> sysfs is a filesystem, no reason to wrap all those commands. >> >> > >> >> > Thanks, I'm asking this more as the pyudev maintainer than as someone >> >> > who actually wants these values. >> >> > >> >> > The funny thing is, I recently found out that the list obtained by >> >> > udev_device_get_sysattr_list_entry () and friends contains so >> >> > called "available" keys, but when those get passed to >> >> > udev_device_get_sysattr_value () the result might be NULL. >> >> > That makes sense in the sense that they might represent files >> >> > that are unreadable. >> >> > >> >> > Now I find out that I can make up keys not in the results of >> >> > udev_device_get_sysattr_list_entry () and pass those to >> >> > udev_device_get_sysattr_value() and get a non-null result. >> >> > >> >> > So, what does "available" mean? Do these sysattr_list_entry() >> >> > methods give any useful information? >> >> >> >> "available" probably means attributes which are direct descendants of >> >> the device. That is, sysattr_list_entry() only lists such direct >> >> descendants, while sysattr_value() allows you to query anything (you >> >> probably can even pass "foo/../../bar/baz"). >> >> >> >> Thanks >> >> David >> >> >> > >> > I think it's yet more complicated than that. For example, >> > 'dm' (for device mapper) is not in the list of available >> > attributes, but 'dm/name' is certainly an attribute that >> > can be read by sysattr_value(). >> >> 'dm' is not an attribute, so it will never be listed as available >> attribute. Directories are never treated as attributes. >> >> Thanks >> David >> > > But "bdi" is listed as an attribute, and is a directory.
Weird. Tom, any comments? _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
