linux-kernel - [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated

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Message-Id: <20210212124354.1.I7084a6235fbcc522b674a6b1db64e4aff8170485@changeid>
Date:   Fri, 12 Feb 2021 12:44:00 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     "Darrick J . Wong" <djwong@...nel.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Ian Lance Taylor <iant@...gle.com>,
        Luis Lozano <llozano@...omium.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Chinner <david@...morbit.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated

Filesystems such as procfs and sysfs generate their content at
runtime. This implies the file sizes do not usually match the
amount of data that can be read from the file, and that seeking
may not work as intended.

This will be useful to disallow copy_file_range with input files
from such filesystems.

Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
---
I first thought of adding a new field to struct file_operations,
but that doesn't quite scale as every single file creation
operation would need to be modified.

 include/linux/fs.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3482146b11b0..5bd58b928e94 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2335,6 +2335,7 @@ struct file_system_type {
 #define FS_ALLOW_IDMAP         32      /* FS has been updated to handle vfs idmappings. */
 #define FS_THP_SUPPORT		8192	/* Remove once all fs converted */
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
+#define FS_GENERATED_CONTENT	65536	/* FS contains generated content */
 	int (*init_fs_context)(struct fs_context *);
 	const struct fs_parameter_spec *parameters;
 	struct dentry *(*mount) (struct file_system_type *, int,
-- 
2.30.0.478.g8a0d178c01-goog