Commits on Apr 25, 2023

1. libct/cg/sd: use systemd version when generating dev props …

   Commit 343951a added a call to os.Stat for the device path
   when generating systemd device properties, to avoid systemd warning for
   non-existing devices. The idea was, since systemd uses stat(2) to look
   up device properties for a given path, it will fail anyway. In addition,
   this allowed to suppress a warning like this from systemd:
   
   > Couldn't stat device /dev/char/10:200
   
   NOTE that this was done because:
    - systemd could not add the rule anyway;
    - runs puts its own set of rules on top of what systemd does.
   
   Apparently, the above change broke some setups, resulting in inability
   to use e.g. /dev/null inside a container. My guess is this is because
   in cgroup v2 we add a second eBPF program, which is not used if the
   first one (added by systemd) returns "access denied".
   
   Next, commit 3b95828 fixed that by adding a call to os.Stat for
   "/sys/"+path (meaning, if "/dev/char/10:200" does not exist, we retry
   with "/sys/dev/char/10:200", and if it exists, proceed with adding a
   device rule with the original (non-"/sys") path).
   
   How that second fix ever worked was a mystery, because the path we gave
   to systemd still doesn't exist.
   
   Well, I think now I know.
   
   Since systemd v240 (commit 74c48bf5a8005f20) device access rules
   specified as /dev/{block|char}/MM:mm are no longer looked up on the
   filesystem, instead, if possible, those are parsed from the string.
   
   So, we need to do different things, depending on systemd version:
   
    - for systemd >= v240, use the /dev/{char,block}/MM:mm as is, without
      doing stat() -- since systemd doesn't do stat() either;
    - for older version, check if the path exists, and skip passing it on
      to systemd otherwise.
    - the check for /sys/dev/{block,char}/MM:mm is not needed in either
      case.
   
   Pass the systemd version to the function that generates the rules, and
   fix it accordingly.
   
   Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
   (cherry picked from commit d7208f5)
   Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

   

   kolyshkin committed Apr 25, 2023
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