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fs: debugfs: differentiate short fops with proxy ops

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Geert reported that my previous short fops debugfs changes
broke m68k, because it only has mandatory alignement of two,
so we can't stash the "is it short" information into the
pointer (as we already did with the "is it real" bit.)

Instead, exploit the fact that debugfs_file_get() called on
an already open file will already find that the fsdata is
no longer the real fops but rather the allocated data that
already distinguishes full/short ops, so only open() needs
to be able to distinguish. We can achieve that by using two
different open functions.

Unfortunately this requires another set of full file ops,
increasing the size by 536 bytes (x86-64), but that's still
a reasonable trade-off given that only converting some of
the wireless stack gained over 28k. This brings the total
cost of this to around 1k, for wins of 28k (all x86-64).

Reported-and-tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/CAMuHMdWu_9-L2Te101w8hU7H_2yobJFPXSwwUmGHSJfaPWDKiQ@mail.gmail.com
Fixes: 8dc6d81c6b ("debugfs: add small file operations for most files")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20241129121536.30989-2-johannes@sipsolutions.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Johannes Berg
2024-11-29 13:15:37 +01:00
committed by Greg Kroah-Hartman
parent 78d4f34e21
commit f8f25893a4
3 changed files with 55 additions and 34 deletions
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11
fs/debugfs/inode.c
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@@ -455,8 +455,7 @@ struct dentry *debugfs_create_file_full(const char *name, umode_t mode,
const struct file_operations *fops)
{
if (WARN_ON((unsigned long)fops &
(DEBUGFS_FSDATA_IS_SHORT_FOPS_BIT |
DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)))
DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
return ERR_PTR(-EINVAL);
return __debugfs_create_file(name, mode, parent, data,
@@ -471,15 +470,13 @@ struct dentry *debugfs_create_file_short(const char *name, umode_t mode,
const struct debugfs_short_fops *fops)
{
if (WARN_ON((unsigned long)fops &
(DEBUGFS_FSDATA_IS_SHORT_FOPS_BIT |
DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)))
DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
return ERR_PTR(-EINVAL);
return __debugfs_create_file(name, mode, parent, data,
fops ? &debugfs_full_proxy_file_operations :
fops ? &debugfs_full_short_proxy_file_operations :
&debugfs_noop_file_operations,
(const void *)((unsigned long)fops |
DEBUGFS_FSDATA_IS_SHORT_FOPS_BIT));
fops);
}
EXPORT_SYMBOL_GPL(debugfs_create_file_short);