diff mbox series

fs: Create anon_inode_getfile_fmode()

Message ID 20240424233859.7640-1-linux@osuchow.ski (mailing list archive)
State New, archived
Headers show
Series fs: Create anon_inode_getfile_fmode() | expand

Commit Message

Dawid Osuchowski April 24, 2024, 11:38 p.m. UTC
Creates an anon_inode_getfile_fmode() function that works similarly to
anon_inode_getfile() with the addition of being able to set the fmode
member.

Signed-off-by: Dawid Osuchowski <linux@osuchow.ski>
---
 fs/anon_inodes.c            | 48 +++++++++++++++++++++++++++++++++++++
 include/linux/anon_inodes.h |  3 +++
 2 files changed, 51 insertions(+)

Comments

Christian Brauner April 25, 2024, 9:57 a.m. UTC | #1
On Thu, Apr 25, 2024 at 01:38:59AM +0200, Dawid Osuchowski wrote:
> Creates an anon_inode_getfile_fmode() function that works similarly to
> anon_inode_getfile() with the addition of being able to set the fmode
> member.

And for what use-case exactly?
Dawid Osuchowski April 25, 2024, 10:13 a.m. UTC | #2
On 4/25/24 11:57, Christian Brauner wrote:
> On Thu, Apr 25, 2024 at 01:38:59AM +0200, Dawid Osuchowski wrote:
>> Creates an anon_inode_getfile_fmode() function that works similarly to
>> anon_inode_getfile() with the addition of being able to set the fmode
>> member.
> 
> And for what use-case exactly?

There was a TODO in the vfio driver [1] to create an interface here that 
would also allow to set fmode, hence this change.

-- Dawid

[1] https://lore.kernel.org/kvm/20240424234147.7840-1-linux@osuchow.ski/T/#u
Al Viro April 25, 2024, 8:25 p.m. UTC | #3
On Thu, Apr 25, 2024 at 11:57:12AM +0200, Christian Brauner wrote:
> On Thu, Apr 25, 2024 at 01:38:59AM +0200, Dawid Osuchowski wrote:
> > Creates an anon_inode_getfile_fmode() function that works similarly to
> > anon_inode_getfile() with the addition of being able to set the fmode
> > member.
> 
> And for what use-case exactly?

There are several places where we might want that -
arch/powerpc/platforms/pseries/papr-vpd.c:488:  file = anon_inode_getfile("[papr-vpd]", &papr_vpd_handle_ops,
fs/cachefiles/ondemand.c:233:   file = anon_inode_getfile("[cachefiles]", &cachefiles_ondemand_fd_fops,
fs/eventfd.c:412:       file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx, flags);
in addition to vfio example Dawid mentions, as well as a couple of
borderline cases in
virt/kvm/kvm_main.c:4404:       file = anon_inode_getfile(name, &kvm_vcpu_stats_fops, vcpu, O_RDONLY);
virt/kvm/kvm_main.c:5092:       file = anon_inode_getfile("kvm-vm-stats",

So something of that sort is probably a good idea.  Said that,
what the hell is __anon_inode_getfile_fmode() for?  It's identical
to exported variant, AFAICS.  And then there's this:

	if (IS_ERR(file))
		goto err;

	file->f_mode |= f_mode;

	return file;

err:
	return file;

a really odd way to spell

	if (!IS_ERR(file))
		file->f_mode |= f_mode;
	return file;
Dawid Osuchowski April 25, 2024, 9:45 p.m. UTC | #4
On 4/25/24 22:25, Al Viro wrote:
> On Thu, Apr 25, 2024 at 11:57:12AM +0200, Christian Brauner wrote:
>> On Thu, Apr 25, 2024 at 01:38:59AM +0200, Dawid Osuchowski wrote:
>>> Creates an anon_inode_getfile_fmode() function that works similarly to
>>> anon_inode_getfile() with the addition of being able to set the fmode
>>> member.
>>
>> And for what use-case exactly?
> 
> There are several places where we might want that -
> arch/powerpc/platforms/pseries/papr-vpd.c:488:  file = anon_inode_getfile("[papr-vpd]", &papr_vpd_handle_ops,
> fs/cachefiles/ondemand.c:233:   file = anon_inode_getfile("[cachefiles]", &cachefiles_ondemand_fd_fops,
> fs/eventfd.c:412:       file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx, flags);
> in addition to vfio example Dawid mentions, as well as a couple of
> borderline cases in
> virt/kvm/kvm_main.c:4404:       file = anon_inode_getfile(name, &kvm_vcpu_stats_fops, vcpu, O_RDONLY);
> virt/kvm/kvm_main.c:5092:       file = anon_inode_getfile("kvm-vm-stats",
> 
> So something of that sort is probably a good idea.  Said that,
> what the hell is __anon_inode_getfile_fmode() for?  It's identical
> to exported variant, AFAICS. 

Thank you for the feedback. I tried emulating what I saw in the other 
functions (which was clearly wrong). Will address this is in next revision.

  And then there's this:
> 
> 	if (IS_ERR(file))
> 		goto err;
> 
> 	file->f_mode |= f_mode;
> 
> 	return file;
> 
> err:
> 	return file;
> 
> a really odd way to spell
> 
> 	if (!IS_ERR(file))
> 		file->f_mode |= f_mode;
> 	return file;

Same for this, will rewrite it based on your suggestion.

-- Dawid
Christian Brauner April 26, 2024, 8:58 a.m. UTC | #5
On Thu, Apr 25, 2024 at 09:25:50PM +0100, Al Viro wrote:
> On Thu, Apr 25, 2024 at 11:57:12AM +0200, Christian Brauner wrote:
> > On Thu, Apr 25, 2024 at 01:38:59AM +0200, Dawid Osuchowski wrote:
> > > Creates an anon_inode_getfile_fmode() function that works similarly to
> > > anon_inode_getfile() with the addition of being able to set the fmode
> > > member.
> > 
> > And for what use-case exactly?
> 
> There are several places where we might want that -
> arch/powerpc/platforms/pseries/papr-vpd.c:488:  file = anon_inode_getfile("[papr-vpd]", &papr_vpd_handle_ops,
> fs/cachefiles/ondemand.c:233:   file = anon_inode_getfile("[cachefiles]", &cachefiles_ondemand_fd_fops,
> fs/eventfd.c:412:       file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx, flags);
> in addition to vfio example Dawid mentions, as well as a couple of
> borderline cases in
> virt/kvm/kvm_main.c:4404:       file = anon_inode_getfile(name, &kvm_vcpu_stats_fops, vcpu, O_RDONLY);
> virt/kvm/kvm_main.c:5092:       file = anon_inode_getfile("kvm-vm-stats",
> 
> So something of that sort is probably a good idea.  Said that,

Ok. It wouldn't be the worst if @Dawid would also sent a follow-patch
converting the obvious cases over to the new helper then.

> what the hell is __anon_inode_getfile_fmode() for?  It's identical

Unrelated to this patch but the other really unpleasant part is that
"make_secure" boolean argument to __anon_inode_getfile() to indicate
allocation of a new inode. That "context_inode" argument is also really
unused for the normal case where the same anon_inode_inode is reused...
IMHO, that should just be split apart. A little more code but it would
make things easier to understand imho...

> to exported variant, AFAICS.  And then there's this:
> 
> 	if (IS_ERR(file))
> 		goto err;
> 
> 	file->f_mode |= f_mode;
> 
> 	return file;
> 
> err:
> 	return file;
> 
> a really odd way to spell
> 
> 	if (!IS_ERR(file))
> 		file->f_mode |= f_mode;
> 	return file;

Yeah.
diff mbox series

Patch

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 0496cb5b6eab..6d61d7d1669a 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -148,6 +148,53 @@  struct file *anon_inode_getfile(const char *name,
 }
 EXPORT_SYMBOL_GPL(anon_inode_getfile);
 
+
+static struct file *__anon_inode_getfile_fmode(const char *name,
+			const struct file_operations *fops,
+			void *priv, int flags, fmode_t f_mode)
+{
+
+	struct file *file;
+
+	file = __anon_inode_getfile(name, fops, priv, flags, NULL, false);
+	if (IS_ERR(file))
+		goto err;
+
+	file->f_mode |= f_mode;
+
+	return file;
+
+err:
+	return file;
+}
+
+/**
+ * anon_inode_getfile_fmode - creates a new file instance by hooking it up to an
+ *                      anonymous inode, and a dentry that describe the "class"
+ *                      of the file
+ *
+ * @name:    [in]    name of the "class" of the new file
+ * @fops:    [in]    file operations for the new file
+ * @priv:    [in]    private data for the new file (will be file's private_data)
+ * @flags:   [in]    flags
+ * @f_mode:  [in]    fmode
+ *
+ * Creates a new file by hooking it on a single inode. This is useful for files
+ * that do not need to have a full-fledged inode in order to operate correctly.
+ * All the files created with anon_inode_getfile() will share a single inode,
+ * hence saving memory and avoiding code duplication for the file/inode/dentry
+ * setup. Allows setting the fmode. Returns the newly created file* or an error
+ * pointer.
+ */
+struct file *anon_inode_getfile_fmode(const char *name,
+				const struct file_operations *fops,
+				void *priv, int flags, fmode_t f_mode)
+{
+	return __anon_inode_getfile_fmode(name, fops, priv,
+					flags, f_mode);
+}
+EXPORT_SYMBOL_GPL(anon_inode_getfile_fmode);
+
 /**
  * anon_inode_create_getfile - Like anon_inode_getfile(), but creates a new
  *                             !S_PRIVATE anon inode rather than reuse the
@@ -271,6 +318,7 @@  int anon_inode_create_getfd(const char *name, const struct file_operations *fops
 	return __anon_inode_getfd(name, fops, priv, flags, context_inode, true);
 }
 
+
 static int __init anon_inode_init(void)
 {
 	anon_inode_mnt = kern_mount(&anon_inode_fs_type);
diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
index 93a5f16d03f3..ee55f9c11a16 100644
--- a/include/linux/anon_inodes.h
+++ b/include/linux/anon_inodes.h
@@ -15,6 +15,9 @@  struct inode;
 struct file *anon_inode_getfile(const char *name,
 				const struct file_operations *fops,
 				void *priv, int flags);
+struct file *anon_inode_getfile_fmode(const char *name,
+				const struct file_operations *fops,
+				void *priv, int flags, unsigned int f_mode);
 struct file *anon_inode_create_getfile(const char *name,
 				       const struct file_operations *fops,
 				       void *priv, int flags,