feat: implement msync syscall as no-op

[wdcui]

Summary

Implements the msync syscall as a no-op that validates arguments and returns success.

Background

Since litebox only supports MAP_PRIVATE mappings (not MAP_SHARED), changes to memory-mapped regions are never written back to the underlying file. Therefore, msync is implemented as a no-op - this is correct per Linux semantics where msync on private mappings has implementation-defined behavior.

This approach is consistent with other advisory syscalls in litebox like readahead and fadvise64 which are also implemented as no-ops.

Implementation

New Types

• MsyncFlags bitflags with MS_ASYNC, MS_INVALIDATE, MS_SYNC

Files Modified

• litebox_common_linux/src/lib.rs: Added MsyncFlags, Msync variant, and dispatch
• litebox_common_linux/src/mm.rs: Implemented sys_msync with validation logic
• litebox_shim_linux/src/lib.rs: Added dispatch case
• litebox_shim_linux/src/syscalls/mm.rs: Added sys_msync wrapper and unit tests

Validation (per Linux semantics)

• addr must be page-aligned → EINVAL
• MS_ASYNC and MS_SYNC are mutually exclusive → EINVAL
• Invalid flags → EINVAL
• Overflow in addr + len → ENOMEM

Tests

• test_msync_basic: Validates MS_SYNC, MS_ASYNC, MS_INVALIDATE, combinations, and zero length
• test_msync_invalid_flags: Validates MS_ASYNC | MS_SYNC returns EINVAL
• test_msync_unaligned_addr: Validates unaligned address returns EINVAL

References

• Linux msync(2) man page
• Linux kernel source: mm/msync.c

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

Click for details

--- failure enum_no_repr_variant_discriminant_changed: enum variant had its discriminant change value ---

Description:
The enum's variant had its discriminant value change. This breaks downstream code that used its value via a numeric cast like `as isize`.
        ref: https://doc.rust-lang.org/reference/items/enumerations.html#assigning-discriminant-values
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/enum_no_repr_variant_discriminant_changed.ron

Failed in:
  variant SyscallRequest::Dup 29 -> 30 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:1990
  variant SyscallRequest::Socket 30 -> 31 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:1995
  variant SyscallRequest::Socketpair 31 -> 32 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2005
  variant SyscallRequest::Connect 32 -> 33 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2011
  variant SyscallRequest::Accept 33 -> 34 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2016
  variant SyscallRequest::Sendto 34 -> 35 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2022
  variant SyscallRequest::Sendmsg 35 -> 36 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2030
  variant SyscallRequest::Recvfrom 36 -> 37 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2035
  variant SyscallRequest::Bind 37 -> 38 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2043
  variant SyscallRequest::Listen 38 -> 39 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2048
  variant SyscallRequest::Setsockopt 39 -> 40 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2052
  variant SyscallRequest::Getsockopt 40 -> 41 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2059
  variant SyscallRequest::Getsockname 41 -> 42 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2066
  variant SyscallRequest::Getpeername 42 -> 43 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2071
  variant SyscallRequest::Uname 43 -> 44 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2076
  variant SyscallRequest::Fcntl 44 -> 45 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2079
  variant SyscallRequest::Getcwd 45 -> 46 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2083
  variant SyscallRequest::EpollCtl 46 -> 47 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2087
  variant SyscallRequest::EpollPwait 47 -> 48 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2093
  variant SyscallRequest::EpollCreate 48 -> 49 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2101
  variant SyscallRequest::Ppoll 49 -> 50 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2105
  variant SyscallRequest::Pselect 50 -> 51 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2112
  variant SyscallRequest::ArchPrctl 51 -> 52 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2120
  variant SyscallRequest::Readlink 52 -> 53 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2123
  variant SyscallRequest::Readlinkat 53 -> 54 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2128
  variant SyscallRequest::Openat 54 -> 55 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2134
  variant SyscallRequest::Ftruncate 55 -> 56 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2140
  variant SyscallRequest::Unlinkat 56 -> 57 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2144
  variant SyscallRequest::Newfstatat 57 -> 58 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2150
  variant SyscallRequest::Eventfd2 58 -> 59 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2163
  variant SyscallRequest::Pipe2 59 -> 60 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2167
  variant SyscallRequest::Clone 60 -> 61 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2171
  variant SyscallRequest::Clone3 61 -> 62 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2174
  variant SyscallRequest::SetThreadArea 62 -> 63 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2179
  variant SyscallRequest::ClockGettime 63 -> 64 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2182
  variant SyscallRequest::ClockGetres 64 -> 65 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2186
  variant SyscallRequest::ClockNanosleep 65 -> 66 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2190
  variant SyscallRequest::Gettimeofday 66 -> 67 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2196
  variant SyscallRequest::Time 67 -> 68 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2200
  variant SyscallRequest::Getrlimit 68 -> 69 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2203
  variant SyscallRequest::Setrlimit 69 -> 70 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2207
  variant SyscallRequest::Prlimit 70 -> 71 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2211
  variant SyscallRequest::SetTidAddress 71 -> 72 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2222
  variant SyscallRequest::Gettid 72 -> 73 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2225
  variant SyscallRequest::SetRobustList 73 -> 74 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2226
  variant SyscallRequest::GetRobustList 74 -> 75 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2229
  variant SyscallRequest::GetRandom 75 -> 76 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2234
  variant SyscallRequest::Getpid 76 -> 77 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2239
  variant SyscallRequest::Getppid 77 -> 78 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2240
  variant SyscallRequest::Getuid 78 -> 79 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2241
  variant SyscallRequest::Geteuid 79 -> 80 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2242
  variant SyscallRequest::Getgid 80 -> 81 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2243
  variant SyscallRequest::Getegid 81 -> 82 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2244
  variant SyscallRequest::Sysinfo 82 -> 83 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2245
  variant SyscallRequest::CapGet 83 -> 84 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2248
  variant SyscallRequest::GetDirent64 84 -> 85 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2252
  variant SyscallRequest::SchedGetAffinity 85 -> 86 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2257
  variant SyscallRequest::SchedYield 86 -> 87 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2262
  variant SyscallRequest::Futex 87 -> 88 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2263
  variant SyscallRequest::Execve 88 -> 89 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2266
  variant SyscallRequest::Umask 89 -> 90 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2271
  variant SyscallRequest::Prctl 90 -> 91 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2274
  variant SyscallRequest::Alarm 91 -> 92 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2277
  variant SyscallRequest::SetITimer 92 -> 93 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2280