diff mbox series

[v20,09/32] tty, proc, kernfs, random: Use direct_splice_read()

Message ID 20230519074047.1739879-10-dhowells@redhat.com (mailing list archive)
State New
Headers show
Series splice, block: Use page pinning and kill ITER_PIPE | expand

Commit Message

David Howells May 19, 2023, 7:40 a.m. UTC 
Use direct_splice_read() for tty, procfs, kernfs and random files rather
than going through generic_file_splice_read() as they just copy the file
into the output buffer and don't splice pages.  This avoids the need for
them to have a ->read_folio() to satisfy filemap_splice_read().

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
cc: Christoph Hellwig <hch@lst.de>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: John Hubbard <jhubbard@nvidia.com>
cc: David Hildenbrand <david@redhat.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Miklos Szeredi <miklos@szeredi.hu>
cc: Arnd Bergmann <arnd@arndb.de>
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
 drivers/char/random.c | 4 ++--
 drivers/tty/tty_io.c  | 4 ++--
 fs/kernfs/file.c      | 2 +-
 fs/proc/inode.c       | 4 ++--
 fs/proc/proc_sysctl.c | 2 +-
 fs/proc_namespace.c   | 6 +++---
 6 files changed, 11 insertions(+), 11 deletions(-)

Comments

Christoph Hellwig May 19, 2023, 8:12 a.m. UTC | #1 
On Fri, May 19, 2023 at 08:40:24AM +0100, David Howells wrote:
>  	.fasync = random_fasync,
>  	.llseek = noop_llseek,
> -	.splice_read = generic_file_splice_read,
> +	.splice_read = direct_splice_read,

Pinging Al (and maybe Linus): is there any good reason to not simply
default to direct_splice_read if ->read_iter is implemented and
->splice_read is not once you remove ITER_PIPE?  As long as we
assure direct_splice_read is simply a ->read_iter into newly
allocated pages I can't think of anything that would go wrong there.
Linus Torvalds May 19, 2023, 4:22 p.m. UTC | #2 
On Fri, May 19, 2023 at 1:12 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> Pinging Al (and maybe Linus): is there any good reason to not simply
> default to direct_splice_read if ->read_iter is implemented and
> ->splice_read is not once you remove ITER_PIPE?

For me, the reason isn't so much technical as "historical pain".

We've had *so* many problems with splice on random file descriptors
that I at some point decided "no splice by default".

Now, admittedly most of the problems were due to the whole set_fs()
ambiguity, which you fixed and no longer exists. So maybe we could go
back to "implement splice by default".

I agree that as long as the default implementation is obviously safe,
it should be ok, and maybe direct_splice_read is that obvious..

           Linus
diff mbox series

Patch

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 253f2ddb8913..2b47b500126c 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1546,7 +1546,7 @@  const struct file_operations random_fops = {
 	.compat_ioctl = compat_ptr_ioctl,
 	.fasync = random_fasync,
 	.llseek = noop_llseek,
-	.splice_read = generic_file_splice_read,
+	.splice_read = direct_splice_read,
 	.splice_write = iter_file_splice_write,
 };
 
@@ -1557,7 +1557,7 @@  const struct file_operations urandom_fops = {
 	.compat_ioctl = compat_ptr_ioctl,
 	.fasync = random_fasync,
 	.llseek = noop_llseek,
-	.splice_read = generic_file_splice_read,
+	.splice_read = direct_splice_read,
 	.splice_write = iter_file_splice_write,
 };
 
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index c84be40fb8df..0b910a2af8e4 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -466,7 +466,7 @@  static const struct file_operations tty_fops = {
 	.llseek		= no_llseek,
 	.read_iter	= tty_read,
 	.write_iter	= tty_write,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= direct_splice_read,
 	.splice_write	= iter_file_splice_write,
 	.poll		= tty_poll,
 	.unlocked_ioctl	= tty_ioctl,
@@ -481,7 +481,7 @@  static const struct file_operations console_fops = {
 	.llseek		= no_llseek,
 	.read_iter	= tty_read,
 	.write_iter	= redirected_tty_write,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= direct_splice_read,
 	.splice_write	= iter_file_splice_write,
 	.poll		= tty_poll,
 	.unlocked_ioctl	= tty_ioctl,
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 40c4661f15b7..be43afa2138d 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -1011,7 +1011,7 @@  const struct file_operations kernfs_file_fops = {
 	.release	= kernfs_fop_release,
 	.poll		= kernfs_fop_poll,
 	.fsync		= noop_fsync,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= direct_splice_read,
 	.splice_write	= iter_file_splice_write,
 };
 
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index f495fdb39151..711f12706469 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -591,7 +591,7 @@  static const struct file_operations proc_iter_file_ops = {
 	.llseek		= proc_reg_llseek,
 	.read_iter	= proc_reg_read_iter,
 	.write		= proc_reg_write,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= direct_splice_read,
 	.poll		= proc_reg_poll,
 	.unlocked_ioctl	= proc_reg_unlocked_ioctl,
 	.mmap		= proc_reg_mmap,
@@ -617,7 +617,7 @@  static const struct file_operations proc_reg_file_ops_compat = {
 static const struct file_operations proc_iter_file_ops_compat = {
 	.llseek		= proc_reg_llseek,
 	.read_iter	= proc_reg_read_iter,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= direct_splice_read,
 	.write		= proc_reg_write,
 	.poll		= proc_reg_poll,
 	.unlocked_ioctl	= proc_reg_unlocked_ioctl,
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 8038833ff5b0..72f1a8ac7802 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -868,7 +868,7 @@  static const struct file_operations proc_sys_file_operations = {
 	.poll		= proc_sys_poll,
 	.read_iter	= proc_sys_read,
 	.write_iter	= proc_sys_write,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= direct_splice_read,
 	.splice_write	= iter_file_splice_write,
 	.llseek		= default_llseek,
 };
diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
index 846f9455ae22..492abbbeff5e 100644
--- a/fs/proc_namespace.c
+++ b/fs/proc_namespace.c
@@ -324,7 +324,7 @@  static int mountstats_open(struct inode *inode, struct file *file)
 const struct file_operations proc_mounts_operations = {
 	.open		= mounts_open,
 	.read_iter	= seq_read_iter,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= direct_splice_read,
 	.llseek		= seq_lseek,
 	.release	= mounts_release,
 	.poll		= mounts_poll,
@@ -333,7 +333,7 @@  const struct file_operations proc_mounts_operations = {
 const struct file_operations proc_mountinfo_operations = {
 	.open		= mountinfo_open,
 	.read_iter	= seq_read_iter,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= direct_splice_read,
 	.llseek		= seq_lseek,
 	.release	= mounts_release,
 	.poll		= mounts_poll,
@@ -342,7 +342,7 @@  const struct file_operations proc_mountinfo_operations = {
 const struct file_operations proc_mountstats_operations = {
 	.open		= mountstats_open,
 	.read_iter	= seq_read_iter,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= direct_splice_read,
 	.llseek		= seq_lseek,
 	.release	= mounts_release,
 };