c - MMAP读写文件

Question

我试图使用 mmap 读取文件，然后对其进行加密，然后将加密写入输出文件。我也在尝试使用 mmap 执行此操作，但是当我运行代码时，它告诉我由于“无效参数”而无法取消映射。

//Open files initialy and obtain a handle to the file.
inputFile = open(inFileName, O_RDONLY, S_IREAD);
outputFile = open(outFileName, O_APPEND | O_CREAT | O_TRUNC | O_WRONLY, S_IWRITE);

//Allocate buffers for encrption.
from = (unsigned char*)malloc(blockSize);
to = (unsigned char*)malloc(blockSize);

mmapWriteBuff = (unsigned char*)malloc(blockSize);
mmapReadBuff = (unsigned char*)malloc(blockSize);

memset(to, 0, blockSize);
memset(from, 0, blockSize);
memset(mmapWriteBuff, 0, blockSize);
memset(mmapReadBuff, 0, blockSize);

//Make sure we have permission to read the file provided.
setFilePermissions(inFileName, PERMISSION_MODE);
setFilePermissions(outFileName, PERMISSION_MODE);

if(encriptParam)
{
    printf("*Encripting file: %s *\n", inFileName);

do//Go through the entire file.
{   
    if(memParam)
    {
            currAmt = lseek(inputFile, blockSize, SEEK_SET);
        mmapReadBuff = mmap(0, blockSize, PROT_READ, MAP_SHARED, inputFile, 0);

        /*
         *This is how you encrypt an input char* buffer "from", of length "len"
         *onto output buffer "to", using key "key".  Jyst pass "iv" and "&n" as
         *shown, and don't forget to actually tell the function to BF_ENCRYPT.
         */

        BF_cfb64_encrypt(mmapReadBuff, mmapWriteBuff, blockSize, &key, iv, &n, BF_ENCRYPT);

        if(currAmt < blockSize)
        {
            writeAmt = lseek(outputFile, currAmt, SEEK_SET);
            mmapWriteBuff = mmap(0, currAmt, PROT_WRITE,  MAP_SHARED, outputFile, 0);                   
            if(errno == EINVAL)
            {
                perror("MMAP failed to start write buffer: ");

                exit(MMAP_IO_ERROR);
            }
        }
        else
        {
            writeAmt = lseek(outputFile, blockSize, SEEK_SET);
            mmapWriteBuff = mmap(0, blockSize, PROT_WRITE, MAP_SHARED, outputFile, 0);                  
            if(errno == EINVAL)
            {
                perror("MMAP failed to start write buffer: ");

                exit(MMAP_IO_ERROR);
            }
        }

        mmapWriteBuff = to;
    }
    else
    {
        currAmt = read(inputFile, from, blockSize);

        /*
         *This is how you encrypt an input char* buffer "from", of length "len"              *onto output buffer "to", using key "key".  Jyst pass "iv" and "n" as
         *shown, and don't forget to actually tell the function to BF_ENCRYT.
        */

        BF_cfb64_encrypt(from, to, blockSize, &key, iv, &n, BF_ENCRYPT);

        if(currAmt < blockSize)
        {
            writeAmt = write(outputFile, to, currAmt);
        }
        else
        {
            writeAmt = write(outputFile, to, blockSize);
        }
    }

    if(memParam)
    {
        //if(currAmt < blockSize)
        //{
        //  if(munmap(mmapWriteBuff, currAmt) == -1)
        //  {
        //      perror("MMAP failed to unmap itself: ");
        //      
        //      exit(MMAP_IO_ERROR);
        //  }
        //  
        //  if(munmap(mmapReadBuff, currAmt) == -1)
        //  {
        //      perror("MMAP failed to unmap itself: ");
        //      
        //      exit(MMAP_IO_ERROR);
        //  }
        //}
        //else
        //{

            if(munmap(mmapReadBuff, blockSize) == -1)
            {
                perror("MMAP Read Buffer failed to unmap itself: ");

                exit(MMAP_IO_ERROR);
            }

            if(munmap(mmapWriteBuff, blockSize) == -1)
            {
                perror("MMAP Write Buffer failed to unmap itself: ");                       
                exit(MMAP_IO_ERROR);
            }


        //}

    }

    memset(to, 0, strlen((char *)to));
    memset(from, 0, strlen((char *)from));
    memset(mmapReadBuff, 0, strlen((char*)mmapReadBuff));
    memset(mmapWriteBuff, 0, strlen((char*)mmapWriteBuff));
    }
    while(currAmt > 0);

    printf("*Saving file: %s *\n", outFileName);

}

Answer 1

一般来说，您可能想尝试设置不带标志的outputFile文件描述符。O_WRONLY使用O_WRONLY标志 formmap()是不够的。

因此，您可能需要更改此设置：

outputFile = open(outFileName, O_APPEND | O_CREAT | O_TRUNC | O_WRONLY, S_IWRITE);

对此：

outputFile = open(outFileName, O_APPEND | O_CREAT | O_TRUNC | O_RDWR, S_IWRITE);

我不是专家mmap()，但我知道您可能希望在打开文件描述符时同时授予它读取和写入权限。

编辑： 您还想尝试将每个mmap()电话都转换(int*)成这样：

mmapReadBuff = (int*)mmap(0, blockSize, PROT_READ, MAP_SHARED, inputFile, 0);