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fdtable: fix longstanding layering violations #75348

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fdtable: fix longstanding layering violations #75348

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Commits on Jul 12, 2024

  1. kernel: types: add k_off_t and k_ssize_t types 

    Define k_off_t to have native support for measuring file offsets
within any kind of file that is supportable in Zephyr.

CONFIG_OFFSET_64BIT is added to allow 32-bit users to force
64-bit offsets, when trading space and speed for flexibility
makes sense for the application.

Define k_ssize_t to have native support for reporting file I/O
sizes along with negative error codes.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>
    Chris Friedt committed Jul 12, 2024
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  2. manifest: optional: update sof to use k_ssize_t 

    Update sof to use k_ssize_t instead of the POSIX ssize_t, thus
avoiding layering violations in core parts of Zephyr.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>
    Chris Friedt committed Jul 12, 2024
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  3. fdtable: remove inappropriate use of POSIX off_t and ssize_t 

    A shortcut was taken many years ago by "cherry-picking" the
POSIX off_t and ssize_t types for use throughout Zephyr.

Additionally, the POSIX header fcntl.h, as well as constants
defined in that header, were being used inappropriately
throughout Zephyr.

Doing so created a dependency cycle: below POSIX's position
in the stack, code depended on POSIX; above POSIX's position
in the stack, code depends on the lower parts.

Such dependency cycles usually result in fragility and
instability of the software stack.

Use the newly defined k_off_t and k_ssize_t types throughout
Zephyr's stack, where off_t and ssize_t were previously used
inappropriately.

Additionally, use ZVFS-prefixed constants instead of their
POSIX counterparts.

Additionally, where appropriate, ensure the POSIX fcntl.h
header is prefixed with <zephyr/posix/fcntl.h>.

We effectively create a mutual dependency to resolve the
cyclic dependency, as described in GitHub issue zephyrproject-rtos#51211.

For clarification, it is inappropriate to use POSIX types or
functions within the kernel, core OS, OS services, or really
anywhere that is not equal to or above POSIX's position in the
software stack.

In other words, if a library uses POSIX, Zephyr's POSIX
implementation cannot depend on that library.

Similarly, if a system service uses POSIX, Zephyr's POSIX
implementation cannot depend on that system service.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>
    Chris Friedt committed Jul 12, 2024
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