fs: move file_start_write() into vfs_iter_write()

All the callers of vfs_iter_write() call file_start_write() just before
calling vfs_iter_write() except for target_core_file's fd_do_rw().

Move file_start_write() from the callers into vfs_iter_write().
fd_do_rw() calls vfs_iter_write() with a non-regular file, so
file_start_write() is a no-op.

This is needed for fanotify "pre content" events.

Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20231122122715.2561213-11-amir73il@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

drivers/block/loop.c

@@ -245,9 +245,7 @@ static int lo_write_bvec(struct file *file, struct bio_vec *bvec, loff_t *ppos)
 
 	iov_iter_bvec(&i, ITER_SOURCE, bvec, 1, bvec->bv_len);
 
-	file_start_write(file);
 	bw = vfs_iter_write(file, &i, ppos, 0);
-	file_end_write(file);
 
 	if (likely(bw ==  bvec->bv_len))
 		return 0;

drivers/target/target_core_file.c

@@ -332,13 +332,11 @@ static int fd_do_rw(struct se_cmd *cmd, struct file *fd,
 	}
 
 	iov_iter_bvec(&iter, is_write, bvec, sgl_nents, len);
-	if (is_write) {
-		file_start_write(fd);
+	if (is_write)
 		ret = vfs_iter_write(fd, &iter, &pos, 0);
-		file_end_write(fd);
-	} else {
+	else
 		ret = vfs_iter_read(fd, &iter, &pos, 0);
-	}
+
 	if (is_write) {
 		if (ret < 0 || ret != data_length) {
 			pr_err("%s() write returned %d\n", __func__, ret);
@@ -469,9 +467,7 @@ fd_execute_write_same(struct se_cmd *cmd)
 	}
 
 	iov_iter_bvec(&iter, ITER_SOURCE, bvec, nolb, len);
-	file_start_write(fd_dev->fd_file);
 	ret = vfs_iter_write(fd_dev->fd_file, &iter, &pos, 0);
-	file_end_write(fd_dev->fd_file);
 
 	kfree(bvec);
 	if (ret < 0 || ret != len) {

fs/coda/file.c

@@ -80,12 +80,10 @@ coda_file_write_iter(struct kiocb *iocb, struct iov_iter *to)
 		goto finish_write;
 
 	inode_lock(coda_inode);
-	file_start_write(host_file);
 	ret = vfs_iter_write(cfi->cfi_container, to, &iocb->ki_pos, 0);
 	coda_inode->i_size = file_inode(host_file)->i_size;
 	coda_inode->i_blocks = (coda_inode->i_size + 511) >> 9;
 	inode_set_mtime_to_ts(coda_inode, inode_set_ctime_current(coda_inode));
-	file_end_write(host_file);
 	inode_unlock(coda_inode);
 
 finish_write:

fs/nfsd/vfs.c

@@ -1186,9 +1186,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 	since = READ_ONCE(file->f_wb_err);
 	if (verf)
 		nfsd_copy_write_verifier(verf, nn);
-	file_start_write(file);
 	host_err = vfs_iter_write(file, &iter, &pos, flags);
-	file_end_write(file);
 	if (host_err < 0) {
 		commit_reset_write_verifier(nn, rqstp, host_err);
 		goto out_nfserr;

fs/overlayfs/file.c

@@ -436,9 +436,7 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 	if (is_sync_kiocb(iocb)) {
 		rwf_t rwf = iocb_to_rw_flags(ifl);
 
-		file_start_write(real.file);
 		ret = vfs_iter_write(real.file, iter, &iocb->ki_pos, rwf);
-		file_end_write(real.file);
 		/* Update size */
 		ovl_file_modified(file);
 	} else {

fs/read_write.c

@@ -839,7 +839,7 @@ ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos,
 EXPORT_SYMBOL(vfs_iter_read);
 
 static ssize_t do_iter_write(struct file *file, struct iov_iter *iter,
-		loff_t *pos, rwf_t flags)
+			     loff_t *pos, rwf_t flags)
 {
 	size_t tot_len;
 	ssize_t ret = 0;
@@ -894,11 +894,18 @@ ssize_t vfs_iocb_iter_write(struct file *file, struct kiocb *iocb,
 EXPORT_SYMBOL(vfs_iocb_iter_write);
 
 ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos,
-		rwf_t flags)
+		       rwf_t flags)
 {
+	int ret;
+
 	if (!file->f_op->write_iter)
 		return -EINVAL;
-	return do_iter_write(file, iter, ppos, flags);
+
+	file_start_write(file);
+	ret = do_iter_write(file, iter, ppos, flags);
+	file_end_write(file);
+
+	return ret;
 }
 EXPORT_SYMBOL(vfs_iter_write);