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ueventd: Add devname sys_name to subsystem, pulling device names from sysfs

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This change introduces a new mode to `subsystem.devname` in `ueventd.rc`
configuration files, which sets the file name to the contents of
`/sys/DEVNAME/name`.

The objective of this change is to help Cuttlefish distinguish between
console devices, which are only different in uevents by initialization
order. Cuttlefish currently relies on `/dev/hvc##` devices which are
created for non-multiport virtio-console devices.

https://cs.android.com/android/platform/superproject/main/+/main:device/google/cuttlefish/shared/config/ueventd.rc;l=18;drc=5204f119d859d3ae5f1a2ee1c6a05ee68d6a28ed

On Cuttlefish we're considering moving to multiport virtio-console
devices ( https://fedoraproject.org/wiki/Features/VirtioSerial ). It
would be possible to rely on device order here as well, but using names
to distinguish devices makes it possible to drop unused devices in the
future, rather than reserving indexes indefinitely.

Multiport virtio-console devices create uevents with DEVNAME=vport#p#
and DEVPATH=.../vport#p#, only exposing the name in a sysfs file.

Bug: 336663898
Test: Attach multiport console, run with `-DLOG_UEVENTS=1`
Test: Introduce ueventd policy using `devname sys_name`
Change-Id: I59632b556db4a47883eab97e90c0e6ca81a9c650
This commit is contained in:
A. Cody Schuffelen 2024-04-23 18:59:00 -07:00
parent 8c7b66629d
commit b479666e3c
3 changed files with 20 additions and 6 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
init/README.ueventd.md
View file

@ -59,9 +59,10 @@ device in. The section takes the below format of
`subsystem_name` is used to match uevent `SUBSYSTEM` value
`devname` takes one of two options
`devname` takes one of three options
1. `uevent_devname` specifies that the name of the node will be the uevent `DEVNAME`
2. `uevent_devpath` specified that the name of the node will be basename uevent `DEVPATH`
2. `uevent_devpath` specifies that the name of the node will be basename uevent `DEVPATH`
3. `sys_name` specifies that the name of the node will be the contents of `/sys/DEVPATH/name`
`dirname` is an optional parameter that specifies a directory within `/dev` where the node will be
created.

17
init/devices.h
View file

@ -82,6 +82,7 @@ class Subsystem {
enum DevnameSource {
DEVNAME_UEVENT_DEVNAME,
DEVNAME_UEVENT_DEVPATH,
DEVNAME_SYS_NAME,
};
Subsystem() {}
@ -92,10 +93,18 @@ class Subsystem {
// Returns the full path for a uevent of a device that is a member of this subsystem,
// according to the rules parsed from ueventd.rc
std::string ParseDevPath(const Uevent& uevent) const {
std::string devname = devname_source_ == DEVNAME_UEVENT_DEVNAME
? uevent.device_name
: android::base::Basename(uevent.path);
std::string devname;
if (devname_source_ == DEVNAME_UEVENT_DEVNAME) {
devname = uevent.device_name;
} else if (devname_source_ == DEVNAME_UEVENT_DEVPATH) {
devname = android::base::Basename(uevent.path);
} else if (devname_source_ == DEVNAME_SYS_NAME) {
if (android::base::ReadFileToString("/sys/" + uevent.path + "/name", &devname)) {
devname.pop_back(); // Remove terminating newline
} else {
devname = uevent.device_name;
}
}
return dir_name_ + "/" + devname;
}

4
init/ueventd_parser.cpp
View file

@ -218,6 +218,10 @@ Result<void> SubsystemParser::ParseDevName(std::vector<std::string>&& args) {
subsystem_.devname_source_ = Subsystem::DEVNAME_UEVENT_DEVPATH;
return {};
}
if (args[1] == "sys_name") {
subsystem_.devname_source_ = Subsystem::DEVNAME_SYS_NAME;
return {};
}
return Error() << "invalid devname '" << args[1] << "'";
}