udev: fix slot based network names on s390

The s390 PCI driver assigns the hotplug slot name from the
function_id attribute of the PCI device using a 8 char hexadecimal
format to match the underlying firmware/hypervisor notation.

Further, there's always a one-to-one mapping between a PCI
function and a hotplug slot, as individual functions can
hot plugged even for multi-function devices.

As the generic matching code will always try to parse the slot
name in /sys/bus/pci/slots as a positive decimal number, either
a wrong value might be produced for ID_NET_NAME_SLOT if
the slot name consists of decimal numbers only, or none at all
if a character in the range from 'a' to 'f' is encountered.

Additionally, the generic code assumes that two interfaces
share a hotplug slot, if they differ only in the function part
of the PCI address. E.g., for an interface with the PCI address
dddd:bb:aa.f, it will match the device to the first slot with
an address dddd:bb:aa. As more than one slot may have this address
for the s390 PCI driver, the wrong slot may be selected.

To resolve this we're adding a new naming schema version with the
flag NAMING_SLOT_FUNCTION_ID, which enables the correct matching
of hotplug slots if the device has an attribute named function_id.
The ID_NET_NAME_SLOT property will only be produced if there's
a file /sys/bus/pci/slots/<slotname> where <slotname> matches
the value of /sys/bus/pci/devices/.../function_id in 8 char
hex notation.

Fixes #19016
See also #19078

man/systemd.net-naming-scheme.xml

@@ -369,6 +369,16 @@
           property.</para></listitem>
         </varlistentry>
 
+        <varlistentry>
+          <term><constant>v249</constant></term>
+
+          <listitem><para>PCI hotplug slot names for the s390 PCI driver are a hexadecimal representation
+          of the <filename>function_id</filename> device attribute. This attribute is now used to build the
+          <varname>ID_NET_NAME_SLOT</varname>. Before that, all slot names were parsed as decimal
+          numbers, which could either result in an incorrect value of the <varname>ID_NET_NAME_SLOT</varname>
+          property or none at all.</para></listitem>
+        </varlistentry>
+
       </variablelist>
 
     <para>Note that <constant>latest</constant> may be used to denote the latest scheme known (to this

src/shared/netif-naming-scheme.c

@@ -13,6 +13,7 @@ static const NamingScheme naming_schemes[] = {
         { "v243", NAMING_V243 },
         { "v245", NAMING_V245 },
         { "v247", NAMING_V247 },
+        { "v249", NAMING_V249 },
         /* … add more schemes here, as the logic to name devices is updated … */
 };
 

src/shared/netif-naming-scheme.h

@@ -32,6 +32,7 @@ typedef enum NamingSchemeFlags {
         NAMING_LABEL_NOPREFIX      = 1 << 7, /* Don't prepend ID_NET_LABEL_ONBOARD with interface type prefix */
         NAMING_NSPAWN_LONG_HASH    = 1 << 8, /* Shorten nspawn interfaces by including 24bit hash, instead of simple truncation  */
         NAMING_BRIDGE_NO_SLOT      = 1 << 9, /* Don't use PCI hotplug slot information if the corresponding device is a PCI bridge */
+        NAMING_SLOT_FUNCTION_ID    = 1 << 10, /* Use function_id if present to identify PCI hotplug slots */
 
         /* And now the masks that combine the features above */
         NAMING_V238 = 0,
@@ -41,6 +42,7 @@ typedef enum NamingSchemeFlags {
         NAMING_V243 = NAMING_V241 | NAMING_NETDEVSIM | NAMING_LABEL_NOPREFIX,
         NAMING_V245 = NAMING_V243 | NAMING_NSPAWN_LONG_HASH,
         NAMING_V247 = NAMING_V245 | NAMING_BRIDGE_NO_SLOT,
+        NAMING_V249 = NAMING_V247 | NAMING_SLOT_FUNCTION_ID,
 
         _NAMING_SCHEME_FLAGS_INVALID = -EINVAL,
 } NamingSchemeFlags;

src/udev/udev-builtin-net_id.c

@@ -345,6 +345,32 @@ static int dev_pci_slot(sd_device *dev, struct netnames *names) {
                 if (sd_device_get_sysname(hotplug_slot_dev, &sysname) < 0)
                         continue;
 
+                /*  The <sysname>/function_id attribute is unique to the s390 PCI driver.
+                    If present, we know that the slot's directory name for this device is
+                    /sys/bus/pci/XXXXXXXX/ where XXXXXXXX is the fixed length 8 hexadecimal
+                    character string representation of function_id.
+                    Therefore we can short cut here and just check for the existence of
+                    the slot directory. As this directory has to exist, we're emitting a
+                    debug message for the unlikely case it's not found.
+                    Note that the domain part of doesn't belong to the slot name here
+                    because there's a 1-to-1 relationship between PCI function and its hotplug
+                    slot.
+                 */
+                if (naming_scheme_has(NAMING_SLOT_FUNCTION_ID) &&
+                    sd_device_get_sysattr_value(hotplug_slot_dev, "function_id", &attr) >= 0) {
+                        int function_id;
+                        _cleanup_free_ char *str;
+
+                        if (safe_atoi(attr, &function_id) >= 0 &&
+                            asprintf(&str, "%s/%08x/", slots, function_id) >= 0 &&
+                            access(str, R_OK) == 0) {
+                                hotplug_slot = function_id;
+                                domain = 0;
+                        } else
+                                log_debug("No matching slot for function_id (%s).", attr);
+                        break;
+                }
+
                 FOREACH_DIRENT_ALL(dent, dir, break) {
                         int i;
                         char str[PATH_MAX];