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。我也试图用mmap来实现这一点，但是当我运行代码时，它告诉我，由于“无效的参数”，它无法取消mmap。

//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，您可能想尝试不使用outputFile标志来设置O_WRONLY文件描述符。仅在O_WRONLY标志中使用mmap()是不够的。

因此，您可能需要更改以下内容：

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mmap()的专家，但我知道您可能希望在打开文件描述符时同时给予它读权限和写权限。

(int*)编辑：编辑:您还想尝试将每个mmap()调用转换为，如下所示：

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