Swatantra-66 opened a new pull request, #20765:
URL: https://github.com/apache/nuttx/pull/20765
## Summary
According to IEEE Std 1003.1 (POSIX), constants prefixed with `_POSIX_*` and
`_POSIX2_*` specify invariant minimum limits that any conforming implementation
must support, not configurable implementation-specific maximums (issue #15464).
Previously, NuttX defined several `_POSIX_*` constants using Kconfig options
(e.g., `CONFIG_NAME_MAX`, `CONFIG_PATH_MAX`, `CONFIG_LIBC_OPEN_MAX`), which
violated POSIX guarantees and caused discrepancies when configurations used
values lower than the standard minimums.
This PR addresses issue #15464 and audits in-tree consumers:
1. **`include/limits.h`**:
- Restored standard POSIX invariant minimums (`_POSIX_NAME_MAX = 14`,
`_POSIX_PATH_MAX = 256`, `_POSIX_ARG_MAX = 4096`, `_POSIX2_LINE_MAX = 2048`,
`_POSIX_OPEN_MAX = 20`, `_POSIX_CHILD_MAX = 25`, `_POSIX_NGROUPS_MAX = 8`,
`_POSIX_STREAM_MAX = 8`, `_POSIX_TZNAME_MAX = 6`, `_POSIX_MQ_PRIO_MAX = 32`,
`_POSIX_SEM_NSEMS_MAX = 256`, `_POSIX_SEM_VALUE_MAX = 32767`,
`_POSIX_CLOCKRES_MIN = 20000000`, `_POSIX_AIO_LISTIO_MAX = 2`).
- Directed implementation limits (`NAME_MAX`, `PATH_MAX`, `ARG_MAX`,
`LINE_MAX`, `OPEN_MAX`, `NGROUPS_MAX`, `AIO_LISTIO_MAX`) directly to their
Kconfig values.
- Raised fallback `CONFIG_PATH_MAX` to `256` so unconfigured builds meet
`_POSIX_PATH_MAX`.
- Defined `STREAM_MAX` as `OPEN_MAX` and set `CLOCK_MAX` to `INT64_MAX`
with `LLONG_MAX` fallback.
- Guarded `PTHREAD_KEYS_MAX` with `#ifndef`.
2. **`include/stdio.h`**:
- Included `<limits.h>`, defined `FILENAME_MAX PATH_MAX` and `FOPEN_MAX
STREAM_MAX` to strictly align file and stream limits (`FOPEN_MAX == STREAM_MAX
== OPEN_MAX`).
3. **`include/sched.h`**:
- Guarded `PTHREAD_KEYS_MAX` with `#ifndef PTHREAD_KEYS_MAX`.
4. **`include/unistd.h`**:
- Defined standard invariant `_POSIX_GETPW_R_SIZE_MAX 1024`.
5. **`fs/vfs/fs_link.c`**:
- Updated link count check against `LINK_MAX` (128) instead of
`_POSIX_LINK_MAX` (8).
6. **`sched/mqueue/mqueue.h`**:
- Set `MQ_PRIO_MAX` to `UCHAR_MAX` instead of `_POSIX_MQ_PRIO_MAX` (32)
to prevent rejecting valid priorities up to 255.
7. **`libs/libc/unistd/lib_pathconf.c` & `lib_sysconf.c`**:
- Updated to report actual runtime limits (`NAME_MAX`, `PIPE_BUF`,
`AIO_MAX`, `CONFIG_LIBC_PASSWD_LINESIZE`).
## Impact
- **POSIX Standard Compliance**: Eliminates contradictions where
applications relying on standard `_POSIX_*` guarantees experienced unexpected
overflows or failures.
- **Embedded Adaptability**: System limits (`NAME_MAX`, `PATH_MAX`,
`OPEN_MAX`, etc.) remain fully user-configurable via Kconfig for
resource-constrained targets.
- **ABI / API**: Fully backward-compatible for existing applications and
configurations.
## Testing
- Verified with `./tools/checkpatch.sh -u HEAD` (0 errors, 0 warnings).
- Verified with `./tools/nxstyle` across all modified files (0 errors, 0
warnings).
Resolves #15464.
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