qemu_get_runtime_dir() returns a dynamically allocated directory path
that is appropriate for storing runtime files. It corresponds to "run"
directory in Unix.

With a tree-wide search, it was found that there are several cases
where such a functionality is implemented so let's have one as a common
utlity function.

A notable feature of qemu_get_runtime_dir() is that it uses
$XDG_RUNTIME_DIR if available. While the function is often called by
executables which requires root privileges, it is still possible that
they are called from a user without privilege to write the system
runtime directory. In fact, I decided to write this patch when I ran
virtiofsd in a Linux namespace created by a normal user and realized
it tries to write the system runtime directory, not writable in this
case. $XDG_RUNTIME_DIR should provide a writable directory in such
cases.

This function does not use qemu_get_local_state_dir() or its logic
for Windows. Actually the implementation of qemu_get_local_state_dir()
for Windows seems not right as it calls g_get_system_data_dirs(),
which refers to $XDG_DATA_DIRS. In Unix terminology, it is basically
"/usr/share", not "/var", which qemu_get_local_state_dir() is intended
to provide. Instead, this function try to use the following in order:
- $XDG_RUNTIME_DIR
- LocalAppData folder
- get_relocated_path(CONFIG_QEMU_LOCALSTATEDIR "/run")

This function does not use g_get_user_runtime_dir() either as it
falls back to g_get_user_cache_dir() when $XDG_DATA_DIRS is not
available. In the case, we rather use:
get_relocated_path(CONFIG_QEMU_LOCALSTATEDIR "/run")

All current callers pass the returned path to g_build_filename(), but
this series does not add a helper to combine those operations. Such a
helper would be complicated due to variadic arguments, and keeping that
out of scope keeps this series focused.

V2 -> V3:
  Rebase to the current master.
  Dropped patch "qga: Remove platform GUID definitions" since it is
  irrelevant.

V1 -> V2:
  Rebased to the current master since Patchew complains.

Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
---
Changes in v5:
- Expanded the patch message.
- Link to v4: https://lore.kernel.org/r/20240716-run-v4-0-5f7a29631168@daynix.com

Changes in v4:
- Rebased.
- Link to v3: https://lore.kernel.org/r/20230921075425.16738-1-akihiko.odaki@daynix.com

---
Akihiko Odaki (8):
      util: Introduce qemu_get_runtime_dir()
      ivshmem-server: Use qemu_get_runtime_dir()
      qga: Use qemu_get_runtime_dir()
      scsi: Use qemu_get_runtime_dir()
      i386/vmsr: Stop using qemu_get_local_state_dir()
      module: Use qemu_get_runtime_dir()
      util: Remove qemu_get_local_state_dir()
      spice-app: Use qemu_get_runtime_dir()

 docs/conf.py                  |  2 ++
 docs/interop/qemu-ga.rst      |  5 +++--
 docs/meson.build              |  6 +++++-
 docs/tools/qemu-pr-helper.rst |  8 ++++----
 include/qemu/module.h         |  2 +-
 include/qemu/osdep.h          | 10 +++++++---
 contrib/ivshmem-server/main.c | 20 ++++++++++++++++----
 qga/main.c                    |  8 ++++----
 scsi/qemu-pr-helper.c         |  6 +++---
 target/i386/kvm/vmsr_energy.c |  6 +++---
 tools/i386/qemu-vmsr-helper.c |  6 +++---
 ui/spice-app.c                |  4 ++--
 util/module.c                 |  3 ++-
 util/oslib-posix.c            |  9 +++++++--
 util/oslib-win32.c            | 26 ++++++++++++++++++++++----
 15 files changed, 84 insertions(+), 37 deletions(-)
---
base-commit: b83371668192a705b878e909c5ae9c1233cbd5fb
change-id: 20240218-run-6f0d91ec7439

Best regards,
--  
Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>