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CA-391656: OCaml C stubs: release runtime lock around all xenctrl calls #4916

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CA-391656: OCaml C stubs: release runtime lock around all xenctrl calls #4916

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Commits on Feb 16, 2023

  1. CA-375276: xenctrlext_stubs.c: xc_get_last_error is not thread safe, … 

    …use just errno which is

It is usually set to XC_INTERNAL_ERROR, except in xenguest, but we have no
bindings for that.

This API might get deleted in upstream Xen too: the error code is stored in the
xenctrl handle, but we made that global per process, and shared among all
threads. Which means that xenctrl calls from different threads can overwrite
each-others' error code.

Also do not use a 'static' buffer, this will no longer be thread safe with
OCaml 5.0 where the runtime lock is per domain instead of global.

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
    @edwintorok
    edwintorok committed Feb 16, 2023
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  2. [maintenance] xa_auth_stubs.c: move free inside the blocking section 

    This is a C call, and might benefit from a bit more parallelism if it inside
the blocking section.

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
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  3. CA-375277: xenctrlext_stubs.c: add missing enter/leave blocking section 

    Most of these calls pass only integers or pointers allocated in C,
so it is safe to release the OCaml runtime lock.

Replace direct passing of Xfm_val/Caml_ba_data_val with storing in a temporary
local variable (the result of Xfm_val or Caml_ba_data_val won't move since they
are C pointers, but the OCaml value passed in as params to these macros might!)

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
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  4. CA-375277: unixpwd_stubs.c: factor out common code and use enter/leav… 

    …e blocking section where possible

unshadow is not thread safe, but the other ones should be.

TODO: double check all C API calls in unixpwd.c with the MT-safe portion of the manpage

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
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  5. C stubs: add a .clang-format 

    We may intend to upstream the xenctrlext stubs to Xen, so it should follow
the Xen CODING_STYLE.
The .clang-format here is based on a version I sent upstream that tries to
follow that coding style.

Signed-off-by: Edwin Török <edwin.torok@cloud.com>
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