[PATCH v3 00/11] memory-backend-file related improvements and VM templating support

[David Hildenbrand]

This is the result of the previous discussion of:
* "[PATCH v2] softmmu/physmem: try opening file readonly before failure
   in file_ram_open" [1]
* "[PATCH v1 0/3] softmmu/physmem: file_ram_open() readonly
   improvements" [2]

After looking into various ways to avoid a new parameter for
memory-backend-file to cleanly support VM templating with R/O files, I
concluded that it might be easier and cleaner to hust have a new parameter.
The alternatives all had their own problems.

Looking back, we could have designed the "readonly=on/off" parameter
slightly differently.

So this series adds a new "rom=on/off/auto" option and wires it up
internally. It uses new internal RAM flags to improve qemu_ram_remap() and
ram_block_discard_range().

Further, improve file_ram_open() with readonly=on and update+add some
documentation.

While working on this and testing some configurations, I realized that
an NVDIMM with label data on ROM does not work as expected (QEMU crashes).
Fix included as patch #1.

v2 -> v3:
- "softmmu/physmem: Distinguish between file access mode and mmap
   protection"
 -> Use !!(ram_flags & RAM_READONLY);
- "backends/hostmem-file: Add "rom" property to support VM templating with
   R/O files"
 -> Improved documentation in qapi/qom.json and qemu-options.hx
- "docs: Start documenting VM templating"
 -> Create proper RST and link it
 -> Add "Security Alert" section
 -> Add MAINTAINER entry
- "softmmu/physmem: Hint that "readonly=on,rom=off" exists when opening
   file R/W for private mapping fails"
 -> Added
- "machine: Improve error message when using default RAM backend id"
 -> Added

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Thiner Logoer <logoerthiner1@163.com>
Cc: "Philippe Mathieu-Daudé" <philmd@linaro.org>
Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Elena Ufimtseva <elena.ufimtseva@oracle.com>
Cc: Jagannathan Raman <jag.raman@oracle.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Ani Sinha <anisinha@redhat.com>
Cc: Xiao Guangrong <xiaoguangrong.eric@gmail.com>
Cc: Daniel Henrique Barboza <danielhb413@gmail.com>
Cc: Greg Kurz <groug@kaod.org>
Cc: Eric Blake <eblake@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: "Daniel P. Berrangé" <berrange@redhat.com>
Cc: Eduardo Habkost <eduardo@habkost.net>

[1] https://lkml.kernel.org/r/20230726145912.88545-1-logoerthiner1@163.com
[2] https://lkml.kernel.org/r/20230807190736.572665-1-david@redhat.com

David Hildenbrand (11):
  nvdimm: Reject writing label data to ROM instead of crashing QEMU
  softmmu/physmem: Distinguish between file access mode and mmap
    protection
  backends/hostmem-file: Add "rom" property to support VM templating
    with R/O files
  softmmu/physmem: Remap with proper protection in qemu_ram_remap()
  softmmu/physmem: Bail out early in ram_block_discard_range() with
    readonly files
  softmmu/physmem: Fail creation of new files in file_ram_open() with
    readonly=true
  softmmu/physmem: Never return directories from file_ram_open()
  docs: Don't mention "-mem-path" in multi-process.rst
  docs: Start documenting VM templating
  softmmu/physmem: Hint that "readonly=on,rom=off" exists when opening
    file R/W for private mapping fails
  machine: Improve error message when using default RAM backend id

 MAINTAINERS                   |   1 +
 backends/hostmem-file.c       |  61 ++++++++++++++++-
 docs/devel/multi-process.rst  |   5 +-
 docs/system/index.rst         |   1 +
 docs/system/vm-templating.rst | 125 ++++++++++++++++++++++++++++++++++
 hw/acpi/nvdimm.c              |  11 ++-
 hw/core/machine.c             |   4 +-
 hw/mem/nvdimm.c               |  10 ++-
 hw/ppc/spapr_nvdimm.c         |   3 +-
 include/exec/memory.h         |  14 ++--
 include/exec/ram_addr.h       |   8 +--
 include/hw/mem/nvdimm.h       |   6 ++
 qapi/qom.json                 |  17 ++++-
 qemu-options.hx               |  16 ++++-
 softmmu/memory.c              |   8 +--
 softmmu/physmem.c             |  93 +++++++++++++++++++------
 16 files changed, 336 insertions(+), 47 deletions(-)
 create mode 100644 docs/system/vm-templating.rst

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2.41.0