[RESEND,BZ,#15132] avoid stat/fstat in statvfs/fstatvfs

From: Eric Wong <normalperson@yhbt.net>

Eric Wong <normalperson@yhbt.net> wrote:
> Ondřej Bílka <neleai@seznam.cz> wrote:
> > > Sorry for the delay.  I've only tested on 3.12+ so far on x86_64.
> > > I'll try to get a VM setup on <2.6.36 soon
> > 
> > Did you test also with these kernels?
> 
> Unfortunately the machine running 2.6.32.x CentOS 6.x kernel
> already had Linux commit 365b18189789bfa1acd9939e6312b8a4b4577b28
> (add f_flags to struct statfs(64)) backported to it :<
> 
> Probably just be easier for me to test with the following kernel patch
> than to get an older kernel running:
> 
> --- a/fs/statfs.c
> +++ b/fs/statfs.c
> @@ -42,7 +42,7 @@ static int flags_by_sb(int s_flags)
>  
>  static int calculate_f_flags(struct vfsmount *mnt)
>  {
> -	return ST_VALID | flags_by_mnt(mnt->mnt_flags) |
> +	return flags_by_mnt(mnt->mnt_flags) |
>  		flags_by_sb(mnt->mnt_sb->s_flags);
>  }
>  

I tested with the above patch applied 3.14 kernel and verified it
correctly falls back to using stat/fstat if the ST_VALID flag is
missing.

On an unpatched 3.14 kernel, the same executables/binaries avoid
stat/fstat when statvfs/fstatvfs are called.

I straced the following program to verify the presence/lack-of
extraneous stat/fstat syscalls after statfs/fstatfs:

  strace /path/to/lib/ld-linux-x86-64.so.2 /tmp/statvfs

-------------------------- /tmp/statvfs.c ----------------------------
#include <sys/statvfs.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
	struct statvfs buf;
	const char *path = argc == 2 ? argv[1] : "/";
	int fd;

	statvfs(path, &buf);
	fd = open(path, O_DIRECTORY, O_RDONLY);
	fstatvfs(fd, &buf);

	return 0;
}

Original patch with updated commit message:
-------------------------------- 8< ---------------------------------
From: Eric Wong <normalperson@yhbt.net>
Subject: [PATCH] avoid stat/fstat in statvfs/fstatvfs

Delay the use of stat/fstat until stat data is required.
When the kernel returns ST_VALID, stat data is not used
by __internal_statvfs.

2014-05-27  Eric Wong  <normalperson@yhbt.net>

	[BZ #15132]
	* sysdeps/unix/sysv/linux/internal_statvfs.c (__statvfs_getflags):
	Call fstat64 or stat64 internally, depending on arguments passed.
	Replace stat buffer argument with file descriptor argument.
	(INTERNAL_STATVFS): Update arguments to match __statvfs_getflags.
	* sysdeps/unix/sysv/linux/fstatvfs.c (fstatvfs):
	Pass fd to __internal_statvfs instead of calling fstat64.
	* sysdeps/unix/sysv/linux/fstatvfs64.c (__fstatvfs64):
	Pass fd to __internal_statvfs64 instead of calling fstat64.
	* sysdeps/unix/sysv/linux/statvfs.c (statvfs):
	Pass -1 to __internal_statvfs instead of calling stat64.
	* sysdeps/unix/sysv/linux/statvfs64.c (__statvfs64):
	Pass -1 to __internal_statvfs64 instead of calling stat64.
---
 sysdeps/unix/sysv/linux/fstatvfs.c         |  4 ++--
 sysdeps/unix/sysv/linux/fstatvfs64.c       | 10 +++-------
 sysdeps/unix/sysv/linux/internal_statvfs.c | 15 ++++++++-------
 sysdeps/unix/sysv/linux/statvfs.c          |  6 ++----
 sysdeps/unix/sysv/linux/statvfs64.c        | 10 +++-------
 5 files changed, 18 insertions(+), 27 deletions(-)

[RESEND,BZ,#15132] avoid stat/fstat in statvfs/fstatvfs

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