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#include <unistd.h>

void vfs_seek(ipc_callid_t rid, ipc_call_t *request)

{

    int fd = (int) IPC_GET_ARG1(*request);

    off_t off = (off_t) IPC_GET_ARG2(*request);

    int whence = (int) IPC_GET_ARG3(*request);

    /*

     * Lookup the file structure corresponding to the file descriptor.

     */

    vfs_file_t *file = vfs_file_get(fd);

    if (!file) {

        ipc_answer_0(rid, ENOENT);

        return;

    }

    off_t newpos;

    futex_down(&file->lock);

    if (whence == SEEK_SET) {

        file->pos = off;

        futex_up(&file->lock);

        ipc_answer_1(rid, EOK, off);

        return;

    }

    if (whence == SEEK_CUR) {

        if (file->pos + off < file->pos) {

            futex_up(&file->lock);

            ipc_answer_0(rid, EOVERFLOW);

            return;

        }

        file->pos += off;

        newpos = file->pos;

        futex_up(&file->lock);

        ipc_answer_1(rid, EOK, newpos);

        return;

    }

    if (whence == SEEK_END) {

        rwlock_reader_lock(&file->node->contents_rwlock);

        size_t size = file->node->size;

        rwlock_reader_unlock(&file->node->contents_rwlock);

        if (size + off < size) {

            futex_up(&file->lock);

            ipc_answer_0(rid, EOVERFLOW);

            return;

        }

        newpos = size + off;

        futex_up(&file->lock);

        ipc_answer_1(rid, EOK, newpos);

        return;

    }

    futex_up(&file->lock);

    ipc_answer_0(rid, EINVAL);

}