Function dfs_file_pread

components/dfs/dfs_v2/src/dfs_file.c:898–944

* @brief Read data from a file at specified offset * * @param[in] file Pointer to the file structure to read from * @param[out] buf Buffer to store the read data * @param[in] len Number of bytes to read * @param[in] offset Offset in the file to start reading from * * @return ssize_t Number of bytes read on success, or negative error code: * -EBADF if invalid file descriptor *

 *         -EINVAL if invalid parameters or not mounted
 */
ssize_t dfs_file_pread(struct dfs_file *file, void *buf, size_t len, off_t offset)
{
    ssize_t ret = -EBADF;

    if (file)
    {
        /* check whether read */
        if (!(dfs_fflags(file->flags) & DFS_F_FREAD))
        {
            ret = -EPERM;
        }
        else if (!file->fops || !file->fops->read)
        {
            ret = -ENOSYS;
        }
        else if (file->vnode && file->vnode->type != FT_DIRECTORY)
        {
            off_t pos = offset;

            ret = rw_verify_area(file, &pos, len);
            if (ret > 0)
            {
                len = ret;

                if (dfs_is_mounted(file->vnode->mnt) == 0)
                {
#ifdef RT_USING_PAGECACHE
                    if (file->vnode->aspace && !(file->flags & O_DIRECT))
                    {
                        ret = dfs_aspace_read(file, buf, len, &pos);
                    }
                    else
#endif
                    {
                        ret = file->fops->read(file, buf, len, &pos);
                    }
                }
                else
                {
                    ret = -EINVAL;
                }
            }
        }
    }

    return ret;
}

/**
 * @brief Read data from a file at current position