From b2858d7d1639c04ca3c54988d76c5f7300b76f1c Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Tue, 19 May 2009 11:37:46 +0200 Subject: [PATCH] splice: fix kmaps in default_file_splice_write() Unfortunately multiple kmap() within a single thread are deadlockable, so writing out multiple buffers with writev() isn't possible. Change the implementation so that it does a separate write() for each buffer. This actually simplifies the code a lot since the splice_from_pipe() helper can be used. This limitation is caused by HIGHMEM pages, and so only affects a subset of architectures and configurations. In the future it may be worth to implement default_file_splice_write() in a more efficient way on configs that allow it. Signed-off-by: Miklos Szeredi Signed-off-by: Jens Axboe --- fs/splice.c | 130 +++++++++------------------------------------------- 1 file changed, 22 insertions(+), 108 deletions(-) diff --git a/fs/splice.c b/fs/splice.c index 41179c0a655b..73766d24f97b 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -535,8 +535,8 @@ static ssize_t kernel_readv(struct file *file, const struct iovec *vec, return res; } -static ssize_t kernel_writev(struct file *file, const struct iovec *vec, - unsigned long vlen, loff_t *ppos) +static ssize_t kernel_write(struct file *file, const char *buf, size_t count, + loff_t pos) { mm_segment_t old_fs; ssize_t res; @@ -544,7 +544,7 @@ static ssize_t kernel_writev(struct file *file, const struct iovec *vec, old_fs = get_fs(); set_fs(get_ds()); /* The cast to a user pointer is valid due to the set_fs() */ - res = vfs_writev(file, (const struct iovec __user *)vec, vlen, ppos); + res = vfs_write(file, (const char __user *)buf, count, &pos); set_fs(old_fs); return res; @@ -1003,120 +1003,34 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out, EXPORT_SYMBOL(generic_file_splice_write); -static struct pipe_buffer *nth_pipe_buf(struct pipe_inode_info *pipe, int n) +static int write_pipe_buf(struct pipe_inode_info *pipe, struct pipe_buffer *buf, + struct splice_desc *sd) { - return &pipe->bufs[(pipe->curbuf + n) % PIPE_BUFFERS]; + int ret; + void *data; + + ret = buf->ops->confirm(pipe, buf); + if (ret) + return ret; + + data = buf->ops->map(pipe, buf, 0); + ret = kernel_write(sd->u.file, data + buf->offset, sd->len, sd->pos); + buf->ops->unmap(pipe, buf, data); + + return ret; } static ssize_t default_file_splice_write(struct pipe_inode_info *pipe, struct file *out, loff_t *ppos, size_t len, unsigned int flags) { - ssize_t ret = 0; - ssize_t total_len = 0; - int do_wakeup = 0; - - pipe_lock(pipe); - while (len) { - struct pipe_buffer *buf; - void *data[PIPE_BUFFERS]; - struct iovec vec[PIPE_BUFFERS]; - unsigned int nr_pages = 0; - unsigned int write_len = 0; - unsigned int now_len = len; - unsigned int this_len; - int i; - - BUG_ON(pipe->nrbufs > PIPE_BUFFERS); - for (i = 0; i < pipe->nrbufs && now_len; i++) { - buf = nth_pipe_buf(pipe, i); - - ret = buf->ops->confirm(pipe, buf); - if (ret) - break; - - data[i] = buf->ops->map(pipe, buf, 0); - this_len = min(buf->len, now_len); - vec[i].iov_base = (void __user *) data[i] + buf->offset; - vec[i].iov_len = this_len; - now_len -= this_len; - write_len += this_len; - nr_pages++; - } - - if (nr_pages) { - ret = kernel_writev(out, vec, nr_pages, ppos); - if (ret == 0) - ret = -EIO; - if (ret > 0) { - len -= ret; - total_len += ret; - } - } - - for (i = 0; i < nr_pages; i++) { - buf = nth_pipe_buf(pipe, i); - buf->ops->unmap(pipe, buf, data[i]); - - if (ret > 0) { - this_len = min_t(unsigned, vec[i].iov_len, ret); - buf->offset += this_len; - buf->len -= this_len; - ret -= this_len; - } - } - - if (ret < 0) - break; - - while (pipe->nrbufs) { - const struct pipe_buf_operations *ops; - - buf = nth_pipe_buf(pipe, 0); - if (buf->len) - break; - - ops = buf->ops; - buf->ops = NULL; - ops->release(pipe, buf); - pipe->curbuf = (pipe->curbuf + 1) % PIPE_BUFFERS; - pipe->nrbufs--; - if (pipe->inode) - do_wakeup = 1; - } - - if (pipe->nrbufs) - continue; - if (!pipe->writers) - break; - if (!pipe->waiting_writers) { - if (total_len) - break; - } - - if (flags & SPLICE_F_NONBLOCK) { - ret = -EAGAIN; - break; - } - - if (signal_pending(current)) { - ret = -ERESTARTSYS; - break; - } - - if (do_wakeup) { - wakeup_pipe_writers(pipe); - do_wakeup = 0; - } - - pipe_wait(pipe); - } - pipe_unlock(pipe); + ssize_t ret; - if (do_wakeup) - wakeup_pipe_writers(pipe); + ret = splice_from_pipe(pipe, out, ppos, len, flags, write_pipe_buf); + if (ret > 0) + *ppos += ret; - return total_len ? total_len : ret; + return ret; } /** -- 2.20.1