Introduce proc_statfs() to replace simple_statfs(), so that
f_bsize queried from statfs() can be consistent w/ the value we
set in s_blocksize.

stat -f /proc/

Before:
    ID: 0        Namelen: 255     Type: proc
Block size: 4096       Fundamental block size: 4096
Blocks: Total: 0          Free: 0          Available: 0
Inodes: Total: 0          Free: 0

After:
    ID: 0        Namelen: 255     Type: proc
Block size: 1024       Fundamental block size: 1024
Blocks: Total: 0          Free: 0          Available: 0
Inodes: Total: 0          Free: 0

Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/proc/inode.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index f495fdb39151..d39e3b9b3135 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -25,6 +25,7 @@
 #include <linux/slab.h>
 #include <linux/mount.h>
 #include <linux/bug.h>
+#include <linux/statfs.h>
 
 #include "internal.h"
 
@@ -176,6 +177,14 @@ static inline const char *hidepid2str(enum proc_hidepid v)
 	return "unknown";
 }
 
+static int proc_statfs(struct dentry *dentry, struct kstatfs *buf)
+{
+	buf->f_type = dentry->d_sb->s_magic;
+	buf->f_bsize = dentry->d_sb->s_blocksize;
+	buf->f_namelen = PROC_NAME_LEN;
+	return 0;
+}
+
 static int proc_show_options(struct seq_file *seq, struct dentry *root)
 {
 	struct proc_fs_info *fs_info = proc_sb_info(root->d_sb);
@@ -195,7 +204,7 @@ const struct super_operations proc_sops = {
 	.free_inode	= proc_free_inode,
 	.drop_inode	= generic_delete_inode,
 	.evict_inode	= proc_evict_inode,
-	.statfs		= simple_statfs,
+	.statfs		= proc_statfs,
 	.show_options	= proc_show_options,
 };
 
-- 
2.25.1

On Tue, Jan 10, 2023 at 11:20:03PM +0800, Chao Yu wrote:
> Introduce proc_statfs() to replace simple_statfs(), so that
> f_bsize queried from statfs() can be consistent w/ the value we
> set in s_blocksize.
> 
> stat -f /proc/
> 
> Before:
>     ID: 0        Namelen: 255     Type: proc
> Block size: 4096       Fundamental block size: 4096
> Blocks: Total: 0          Free: 0          Available: 0
> Inodes: Total: 0          Free: 0
> 
> After:
>     ID: 0        Namelen: 255     Type: proc
> Block size: 1024       Fundamental block size: 1024
> Blocks: Total: 0          Free: 0          Available: 0
> Inodes: Total: 0          Free: 0

4096 is better value is in fact.

seq_files allocate 1 page and fill it, therefore reading less than
PAGE_SIZE from /proc is mostly waste of syscalls.

I doubt anything uses f_bsize.

BTW this patch is not self contained.

On 2023/1/11 1:58, Alexey Dobriyan wrote:
> On Tue, Jan 10, 2023 at 11:20:03PM +0800, Chao Yu wrote:
>> Introduce proc_statfs() to replace simple_statfs(), so that
>> f_bsize queried from statfs() can be consistent w/ the value we
>> set in s_blocksize.
>>
>> stat -f /proc/
>>
>> Before:
>>      ID: 0        Namelen: 255     Type: proc
>> Block size: 4096       Fundamental block size: 4096
>> Blocks: Total: 0          Free: 0          Available: 0
>> Inodes: Total: 0          Free: 0
>>
>> After:
>>      ID: 0        Namelen: 255     Type: proc
>> Block size: 1024       Fundamental block size: 1024
>> Blocks: Total: 0          Free: 0          Available: 0
>> Inodes: Total: 0          Free: 0
> 
> 4096 is better value is in fact.
> 
> seq_files allocate 1 page and fill it, therefore reading less than
> PAGE_SIZE from /proc is mostly waste of syscalls.

Ah, thanks for correcting me, so, how about updating .s_blocksize and
.s_blocksize_bits to PAGE_SIZE and PAGE_SHIFT?

> 
> I doubt anything uses f_bsize.
> 
> BTW this patch is not self contained.

Oh, yes, my bad.

Thanks,