[PATCH v2] fs: Create anon_inode_getfile_fmode()

[PATCH v2] fs: Create anon_inode_getfile_fmode()

[Dawid Osuchowski]

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>
---
Changes since v1:
* removed __anon_inode_create_getfile_fmode()
* streamlined if statement and got rid of goto
---
 fs/anon_inodes.c            | 33 +++++++++++++++++++++++++++++++++
 include/linux/anon_inodes.h |  3 +++
 2 files changed, 36 insertions(+)

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 0496cb5b6eab..42bd1cb7c9cd 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -148,6 +148,38 @@ struct file *anon_inode_getfile(const char *name,
 }
 EXPORT_SYMBOL_GPL(anon_inode_getfile);
 
+/**
+ * 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)
+{
+	struct file *file;
+
+	file = __anon_inode_getfile(name, fops, priv, flags, NULL, false);
+	if (!IS_ERR(file))
+		file->f_mode |= f_mode;
+
+	return file;
+}
+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 +303,7 @@ 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,
-- 
2.44.0

Re: [PATCH v2] fs: Create anon_inode_getfile_fmode()

[Al Viro]

On Thu, Apr 25, 2024 at 11:58:03PM +0200, Dawid Osuchowski wrote:
> +struct file *anon_inode_getfile_fmode(const char *name,
> +				const struct file_operations *fops,
> +				void *priv, int flags, fmode_t f_mode)
						       ^^^^^^^
> +struct file *anon_inode_getfile_fmode(const char *name,
> +				const struct file_operations *fops,
> +				void *priv, int flags, unsigned int f_mode);
						       ^^^^^^^^^^^^

They ought to match (and fmode_t is the right type here).

Re: [PATCH v2] fs: Create anon_inode_getfile_fmode()

[Dawid Osuchowski]

On 4/26/24 00:03, Al Viro wrote:
> On Thu, Apr 25, 2024 at 11:58:03PM +0200, Dawid Osuchowski wrote:
>> +struct file *anon_inode_getfile_fmode(const char *name,
>> +				const struct file_operations *fops,
>> +				void *priv, int flags, fmode_t f_mode)
> 						       ^^^^^^^
>> +struct file *anon_inode_getfile_fmode(const char *name,
>> +				const struct file_operations *fops,
>> +				void *priv, int flags, unsigned int f_mode);
> 						       ^^^^^^^^^^^^
> 
> They ought to match (and fmode_t is the right type here).

Should I include the <linux/fs.h> header (or a different one) into 
anon_inodes.h to get the fmode_t type or can I copy the typedef directly 
as a sort of "forward declare" instead?

The latter would mean something like this:

	struct inode;
+	typedef unsigned int fmode_t;

-- Dawid

Re: [PATCH v2] fs: Create anon_inode_getfile_fmode()

[Al Viro]

On Fri, Apr 26, 2024 at 12:15:52AM +0200, Dawid Osuchowski wrote:
> On 4/26/24 00:03, Al Viro wrote:
> > On Thu, Apr 25, 2024 at 11:58:03PM +0200, Dawid Osuchowski wrote:
> > > +struct file *anon_inode_getfile_fmode(const char *name,
> > > +				const struct file_operations *fops,
> > > +				void *priv, int flags, fmode_t f_mode)
> > 						       ^^^^^^^
> > > +struct file *anon_inode_getfile_fmode(const char *name,
> > > +				const struct file_operations *fops,
> > > +				void *priv, int flags, unsigned int f_mode);
> > 						       ^^^^^^^^^^^^
> > 
> > They ought to match (and fmode_t is the right type here).
> 
> Should I include the <linux/fs.h> header (or a different one) into
> anon_inodes.h to get the fmode_t type or can I copy the typedef directly as
> a sort of "forward declare" instead?
> 
> The latter would mean something like this:
> 
> 	struct inode;
> +	typedef unsigned int fmode_t;

linux/types.h, if anything.

Re: [PATCH v2] fs: Create anon_inode_getfile_fmode()

[Dawid Osuchowski]

On 4/26/24 00:31, Al Viro wrote:

> linux/types.h, if anything.

Thanks, will address in next revision.

-- Dawid