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Date:   Tue, 6 Jun 2023 11:38:35 -0700
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Lucas De Marchi <lucas.de.marchi@gmail.com>
Cc:     linux-modules@vger.kernel.org
Subject: Re: [PATCH 5/5] libkmod: Use kernel decompression when available
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References: <20230601224001.23397-1-lucas.de.marchi@gmail.com>
 <20230601224001.23397-6-lucas.de.marchi@gmail.com>
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On Thu, Jun 01, 2023 at 03:40:01PM -0700, Lucas De Marchi wrote:
> With the recent changes to bypass loading the file it's possible to
> reduce the work in userspace and delegating it to the kernel. Without
> any compression to illustrate:
> 
> Before:
> 	read(3, "\177ELF\2\1", 6)               = 6
> 	lseek(3, 0, SEEK_SET)                   = 0
> 	newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=238592, ...}, AT_EMPTY_PATH) = 0
> 	mmap(NULL, 238592, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fd85cbd1000
> 	finit_module(3, "", 0)                  = 0
> 	munmap(0x7fd85cbd1000, 238592)          = 0
> 	close(3)                                = 0
> 
> After:
> 	read(3, "\177ELF\2\1", 6)               = 6
> 	lseek(3, 0, SEEK_SET)                   = 0
> 	finit_module(3, "", 0)                  = 0
> 	close(3)                                = 0

It's not clear to me how the patches did the above, in particular
avoiding the newfstatat() for the non-decompression use case.

  Luis