Function dfs_seq_read

components/dfs/dfs_v2/src/dfs_seq_file.c:175–318

* @brief Read data from sequence file * * @param[in] file Pointer to the file structure * @param[out] buf Buffer to store the read data * @param[in] size Size of the buffer in bytes * @param[in,out] pos Current file position (updated after read) * * @return ssize_t Number of bytes read on success, negative error code on failure: * -EFAULT if buffer error occurs * -ENOMEM i

 *          7. Copy data to user buffer and update positions
 */
ssize_t dfs_seq_read(struct dfs_file *file, void *buf, size_t size, off_t *pos)
{
    struct dfs_seq_file *seq = file->data;
    size_t copied = 0;
    size_t n;
    void *p;
    int err = 0;

    if (!size)
        return 0;

    rt_mutex_take(&seq->lock, RT_WAITING_FOREVER);

    /*
     * if request is to read from zero offset, reset iterator to first
     * record as it might have been already advanced by previous requests
     */
    if (*pos == 0)
    {
        seq->index = 0;
        seq->count = 0;
    }

    /* Don't assume ki_pos is where we left it */
    if (*pos != seq->read_pos)
    {
        while ((err = dfs_seq_traverse(seq, *pos)) == -EAGAIN)
            ;
        if (err)
        {
            /* With prejudice... */
            seq->read_pos = 0;
            seq->index = 0;
            seq->count = 0;
            goto Done;
        }
        else
        {
            seq->read_pos = *pos;
        }
    }

    /* grab buffer if we didn't have one */
    if (!seq->buf)
    {
        seq->buf = dfs_seq_alloc(seq->size = PAGE_SIZE);
        if (!seq->buf)
            goto Enomem;
    }
    /* something left in the buffer - copy it out first */
    if (seq->count)
    {
        n = seq->count > size ? size : seq->count;
        rt_memcpy((char *)buf + copied, seq->buf + seq->from, n);
        size -= n;
        seq->count -= n;
        seq->from += n;
        copied += n;