Function pread

components/dfs/dfs_v2/src/dfs_posix.c:1385–1418

* this function is a POSIX compliant version, which will read specified data * buffer length for an open file descriptor. * * @param fd the file descriptor. * @param buf the buffer to save the read data. * @param len the maximal length of data buffer * @param offset the file pos * * @return the actual read data buffer length. If the returned value is 0, it * may be reach the end of file,

 * may be reach the end of file, please check errno.
 */
ssize_t pread(int fd, void *buf, size_t len, off_t offset)
{
    ssize_t result;
    off_t fpos;
    struct dfs_file *file;

    if (buf == NULL)
    {
        rt_set_errno(-EBADF);
        return -1;
    }

    file = fd_get(fd);
    if (file == NULL)
    {
        rt_set_errno(-EBADF);

        return -1;
    }

    /* fpos lock */
    fpos = dfs_file_get_fpos(file);
    result = dfs_file_pread(file, buf, len, offset);
    /* fpos unlock */
    dfs_file_set_fpos(file, fpos);
    if (result < 0)
    {
        rt_set_errno(result);

        return -1;
    }

    return result;
}
RTM_EXPORT(pread);

/**