AuroraRuntime/Source/IO/FS/FileAdvisory.Unix.cpp

/***
    Copyright (C) 2022 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: FileAdvisory.Unix.cpp
    Date: 2022-1-29
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include "FS.hpp"
#include "FileAdvisory.hpp"
#include "FileAdvisory.Unix.hpp"
#include <sys/file.h>

#if defined(AURORA_COMPILER_CLANG)
    // warning: enumeration values 'kEnumCount' and 'kEnumInvalid' not handled in switch [-Wswitch
    #pragma clang diagnostic ignored "-Wswitch"
    // Yea, I don't give a shit.
#endif

namespace Aurora::IO::FS
{
    bool ApplyDumbAdvisoryLock(int fd, EFileAdvisoryLockLevel level)
    {
    #if !defined(AURORA_IS_LINUX_DERIVED)
        int operation = LOCK_NB;

        switch (level)
        {
        case EFileAdvisoryLockLevel::eEnumCount:
        case EFileAdvisoryLockLevel::eNoSafety:
            return true;
        case EFileAdvisoryLockLevel::eBlockWrite:
            operation |= LOCK_SH;
            break;
        case EFileAdvisoryLockLevel::eBlockReadWrite:
            operation |= LOCK_EX;
            break;
        }

        // Assume:
        // "Furthermore, the lock is release either by an explicit LOCK_UN
        // operation on any of these duplicate file descriptors, or when
        // all such file descriptors have been closed"
        
        return ::flock(fd, operation) == 0;
    #else
        // Linux
        int lease {};

        switch (level)
        {
        case EFileAdvisoryLockLevel::eEnumCount:
        case EFileAdvisoryLockLevel::eNoSafety:
            return true;
        case EFileAdvisoryLockLevel::eBlockWrite:
            lease = F_RDLCK;
            break;
        case EFileAdvisoryLockLevel::eBlockReadWrite:
            lease = F_WRLCK;
            break;
        }

        // Ignore warning bc idc
        // I assume c++ compilers under posix land allow for struct init the c way 
        struct flock lck = 
        {
            .l_whence = SEEK_SET,
            .l_start = 0,
            .l_len = 0,
            .l_type = lease
        };

        // Assume this is true:
        // *  If a process closes any file descriptor referring to a file,
        //    then all of the process's locks on that file are released,
        //    regardless of the file descriptor(s) on which the locks were
        //    obtained.  This is bad: it means that a process can lose its
        //    locks on a file such as /etc/passwd or /etc/mtab when for some
        //    reason a library function decides to open, read, and close the
        //    same file.
        // [...]
        //
        // Open file description locks solve both of these problems.
        // 
        // OFD's description implies it inherits non-ofd behaviour
        // I wanted to confirm a l_len zero would work to lock all contents,
        // even on expansion of the file. The docs didn't mention anything;
        // however, I don't really see any real difference len processing in 
        // the kernel. Furthermore, I saw the kernels implementation checking
        // for MAX_OFFSET of int type (-1) before overloading l_len with zero.
        //
        // I assume this will work. Linux locking is trash.
        return ::fcntl(fd, F_OFD_SETLK, &lck) == 0;
    #endif
    }

    bool ApplyFileSectionLock(AuSPtr<IIOHandle> pHandle,
                              EFileAdvisoryLockLevel level,
                              AuUInt64 uOffset,
                              AuUInt64 uLength)
    {
        int lease {};

        auto opt = pHandle->GetOSHandleSafe();
        if (!opt)
        {
            SysPushErrorIOResourceRejected();
            return false;
        }

        int fd = (int)opt.ValueOr((int)-1);
        if (fd == -1)
        {
            SysPushErrorIOResourceRejected();
            return false;
        }

        switch (level)
        {
        case EFileAdvisoryLockLevel::eEnumCount:
        case EFileAdvisoryLockLevel::eNoSafety:
            return true;
        case EFileAdvisoryLockLevel::eBlockWrite:
            lease = F_RDLCK;
            break;
        case EFileAdvisoryLockLevel::eBlockReadWrite:
            lease = F_WRLCK;
            break;
        }

        struct flock lck = 
        {
            .l_whence = SEEK_SET,
            .l_start = uLength,
            .l_len = uOffset,
            .l_type = lease
        };

    #if defined(AURORA_IS_LINUX_DERIVED)
        return ::fcntl(fd, F_OFD_SETLK, &lck) == 0;
    #else
        return ::fcntl(fd, F_SETLK, &lck) == 0;
    #endif
    }

    bool UnapplyFileSectionLock(AuSPtr<IIOHandle> pHandle,
                                AuUInt64 uOffset,
                                AuUInt64 uLength)
    {
        auto opt = pHandle->GetOSHandleSafe();
        if (!opt)
        {
            SysPushErrorIOResourceRejected();
            return false;
        }

        int fd = (int)opt.ValueOr((int)-1);
        if (fd == -1)
        {
            SysPushErrorIOResourceRejected();
            return false;
        }

        struct flock lck = 
        {
            .l_whence = SEEK_SET,
            .l_start = uLength,
            .l_len = uOffset,
            .l_type = F_UNLCK
        };

    #if defined(AURORA_IS_LINUX_DERIVED)
        return ::fcntl(fd, F_OFD_SETLK, &lck) == 0;
    #else
        return ::fcntl(fd, F_SETLK, &lck) == 0;
    #endif
    }
}