[17/23] proc: add a read_iter method to proc proc_ops
diff mbox series

Message ID 20200701200951.3603160-18-hch@lst.de
State New
Headers show
Series
  • [01/23] cachefiles: switch to kernel_write
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Commit Message

Christoph Hellwig July 1, 2020, 8:09 p.m. UTC
This will allow proc files to implement iter read semantics.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/proc/inode.c         | 28 ++++++++++++++++++++++++++++
 include/linux/proc_fs.h |  1 +
 2 files changed, 29 insertions(+)

Comments

Al Viro July 1, 2020, 9:27 p.m. UTC | #1
On Wed, Jul 01, 2020 at 10:09:45PM +0200, Christoph Hellwig wrote:
> This will allow proc files to implement iter read semantics.

*UGH*

You are introducing file_operations with both ->read() and ->read_iter();
worse, in some cases they are not equivalent.  Sure, ->read() takes
precedence right now, but...  why not a separate file_operations for
->read_iter-capable files?

I really hate the fallbacks of that sort - they tend to be brittle
as hell.  And while we are at it, I'm not sure that your iter_read() 
has good cause to be non-static.
Christoph Hellwig July 2, 2020, 5:18 a.m. UTC | #2
On Wed, Jul 01, 2020 at 10:27:51PM +0100, Al Viro wrote:
> On Wed, Jul 01, 2020 at 10:09:45PM +0200, Christoph Hellwig wrote:
> > This will allow proc files to implement iter read semantics.
> 
> *UGH*
> 
> You are introducing file_operations with both ->read() and ->read_iter();
> worse, in some cases they are not equivalent.  Sure, ->read() takes
> precedence right now, but...  why not a separate file_operations for
> ->read_iter-capable files?

I looked at that initially.  We'd need to more instances as there
already are two due to compat stuff.  If that is preferably I can
switch to that version.

> I really hate the fallbacks of that sort - they tend to be brittle
> as hell.  And while we are at it, I'm not sure that your iter_read() 
> has good cause to be non-static.

The other user of it is seq_file, which as-is should go away, but
will probably keep the occasional version of it in the caller.  I just
got really tired of reimplementing it a few times.
Christoph Hellwig July 2, 2020, 7:30 a.m. UTC | #3
On Thu, Jul 02, 2020 at 07:18:11AM +0200, Christoph Hellwig wrote:
> On Wed, Jul 01, 2020 at 10:27:51PM +0100, Al Viro wrote:
> > On Wed, Jul 01, 2020 at 10:09:45PM +0200, Christoph Hellwig wrote:
> > > This will allow proc files to implement iter read semantics.
> > 
> > *UGH*
> > 
> > You are introducing file_operations with both ->read() and ->read_iter();
> > worse, in some cases they are not equivalent.  Sure, ->read() takes
> > precedence right now, but...  why not a separate file_operations for
> > ->read_iter-capable files?
> 
> I looked at that initially.  We'd need to more instances as there
> already are two due to compat stuff.  If that is preferably I can
> switch to that version.
> 
> > I really hate the fallbacks of that sort - they tend to be brittle
> > as hell.  And while we are at it, I'm not sure that your iter_read() 
> > has good cause to be non-static.
> 
> The other user of it is seq_file, which as-is should go away, but
> will probably keep the occasional version of it in the caller.  I just
> got really tired of reimplementing it a few times.

I've force puhed a new version to the existing location:

   git://git.infradead.org/users/hch/misc.git set_fs-rw

That gets uses separate ops in proc after a few preparational cleanups
and rid of the iter_read() patch entirely.  Let me know what you think,
I don't really want to send the whole patch bomb again already.

Gitweb is also avaiable here:

   http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/set_fs-rw

Patch
diff mbox series

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 28d6105e908e4c..fa86619cebc2be 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -297,6 +297,29 @@  static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence)
 	return rv;
 }
 
+static ssize_t pde_read_iter(struct proc_dir_entry *pde, struct kiocb *iocb,
+		struct iov_iter *iter)
+{
+	if (!pde->proc_ops->proc_read_iter)
+		return -EINVAL;
+	return pde->proc_ops->proc_read_iter(iocb, iter);
+}
+
+static ssize_t proc_reg_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct proc_dir_entry *pde = PDE(file_inode(iocb->ki_filp));
+	ssize_t ret;
+
+	if (pde_is_permanent(pde))
+		return pde_read_iter(pde, iocb, iter);
+
+	if (!use_pde(pde))
+		return -EIO;
+	ret = pde_read_iter(pde, iocb, iter);
+	unuse_pde(pde);
+	return ret;
+}
+
 static ssize_t pde_read(struct proc_dir_entry *pde, struct file *file, char __user *buf, size_t count, loff_t *ppos)
 {
 	typeof_member(struct proc_ops, proc_read) read;
@@ -312,6 +335,9 @@  static ssize_t proc_reg_read(struct file *file, char __user *buf, size_t count,
 	struct proc_dir_entry *pde = PDE(file_inode(file));
 	ssize_t rv = -EIO;
 
+	if (pde->proc_ops->proc_read_iter)
+		return iter_read(file, buf, count, ppos, proc_reg_read_iter);
+
 	if (pde_is_permanent(pde)) {
 		return pde_read(pde, file, buf, count, ppos);
 	} else if (use_pde(pde)) {
@@ -569,6 +595,7 @@  static int proc_reg_release(struct inode *inode, struct file *file)
 static const struct file_operations proc_reg_file_ops = {
 	.llseek		= proc_reg_llseek,
 	.read		= proc_reg_read,
+	.read_iter	= proc_reg_read_iter,
 	.write		= proc_reg_write,
 	.poll		= proc_reg_poll,
 	.unlocked_ioctl	= proc_reg_unlocked_ioctl,
@@ -585,6 +612,7 @@  static const struct file_operations proc_reg_file_ops = {
 static const struct file_operations proc_reg_file_ops_no_compat = {
 	.llseek		= proc_reg_llseek,
 	.read		= proc_reg_read,
+	.read_iter	= proc_reg_read_iter,
 	.write		= proc_reg_write,
 	.poll		= proc_reg_poll,
 	.unlocked_ioctl	= proc_reg_unlocked_ioctl,
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index d1eed1b4365172..97b3f5f06db9d8 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -30,6 +30,7 @@  struct proc_ops {
 	unsigned int proc_flags;
 	int	(*proc_open)(struct inode *, struct file *);
 	ssize_t	(*proc_read)(struct file *, char __user *, size_t, loff_t *);
+	ssize_t (*proc_read_iter)(struct kiocb *, struct iov_iter *);
 	ssize_t	(*proc_write)(struct file *, const char __user *, size_t, loff_t *);
 	loff_t	(*proc_lseek)(struct file *, loff_t, int);
 	int	(*proc_release)(struct inode *, struct file *);