Re: [PATCH 4/5] mm: shmem: Convert shmem_enabled_show to use sysfs_emit_at

[Matthew Wilcox]

On Sun, Nov 01, 2020 at 01:43:13PM -0800, Joe Perches wrote:
> > Why did you change this?
> 
> Are you asking about the function argument alignment or the commit message?

The indentation.  Don't change the fucking indentation, Joe.

> > Look, this isn't performance sensitive code.  Just do something simple.
> > 
> >             if (shmem_huge == values[i])
> >                     buf += sysfs_emit(buf, "[%s]",
> >                                     shmem_format_huge(values[i]));
> >             else
> >                     buf += sysfs_emit(buf, "%s",
> >                                     shmem_format_huge(values[i]));
> >             if (i == ARRAY_SIZE(values) - 1)
> >                     buf += sysfs_emit(buf, "\n");
> >             else
> >                     buf += sysfs_emit(buf, " ");
> > 
> > Shame there's no sysfs_emitc, but there you go.
> 
> I think what's there is simple.

Again, you're wrong.

> And your suggested code doesn't work.
> sysfs_emit is used for single emits.
> sysfs_emit_at is used for multiple emits.

Oh, ugh, sysfs_emit() should be able to work on a buffer that isn't
page aligned.  Greg, how about this?

+++ b/fs/sysfs/file.c
@@ -722,13 +722,13 @@ int sysfs_emit(char *buf, const char *fmt, ...)
 {
        va_list args;
        int len;
+       int start = offset_in_page(buf);
 
-       if (WARN(!buf || offset_in_page(buf),
-                "invalid sysfs_emit: buf:%p\n", buf))
+       if (WARN(!buf, "invalid sysfs_emit: buf:%p\n", buf))
                return 0;
 
        va_start(args, fmt);
-       len = vscnprintf(buf, PAGE_SIZE, fmt, args);
+       len = vscnprintf(buf, PAGE_SIZE - start, fmt, args);
        va_end(args);
 
        return len;