So far, we have documented that the AC_SYS_LARGEFILE macro (from module
'largefile') is useful for accessing files > 2 GiB.
Now, Dmitry Levin points out in [1] that this macro is also needed to
make stat() and fstat() "work properly on file systems with 64-bit inodes".
I think what he means is the "64 bit inode problem": stat(), lstat(),
fstat() fail with EOVERFLOW if
- the Linux file system has 64-bit inodes enabled,
- the file's inode happens to not fit in 32 bits,
- the application is a 32-bit Linux/x86 application (possibly running
on Linux/x86_64).
In fact, this is what I see in /usr/include/asm/stat.h on a Linux/x86_64
machine:
#ifdef __i386__
struct stat {
...
unsigned long st_ino; /* 32 bits */
...
};
struct stat64 {
...
unsigned long __st_ino; /* 32 bits */
...
unsigned long long st_ino; /* 64 bits */
...
};
#else
struct stat {
...
__kernel_ulong_t st_ino;
..
};
#endif
It confirms what was said in that article and that using stat64() instead
of stat() will fix the issue.
Which file systems are affected?
- Ext4 apparently not [3][4]
- XFS [5]
- NFS [6]
Are other OSes affected?
- FreeBSD is said to have achieved 64-bit inode support "while retaining
backwards compatibility" - so, no AC_SYS_LARGEFILE is needed here. [7]
[1] https://lists.gnu.org/archive/html/bug-gettext/2020-01/msg00001.html
[2] https://www.mjr19.org.uk/sw/inodes64.html
[3] https://steamcommunity.com/app/221410/discussions/0/620695877288637183/
[4] https://www.kernel.org/doc/html/latest/filesystems/ext4/index.html
[5] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1361637
[6]
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/4/html/Release_Notes/U7/ppc/ar01s04.html
[7]
https://www.phoronix.com/scan.php?page=news_item&px=FreeBSD-64-bit-Inodes-ino64
I'm therefore adding this doc update in gnulib. Does it sound correct?
The autoconf documentation of AC_SYS_LARGEFILE would also need to be updated.
2020-01-03 Bruno Haible <br...@clisp.org>
doc: Mention the 64-bit inode number problem.
* m4/largefile.m4 (AC_SYS_LARGEFILE): Mention that this macro fixes the
64-bit inode number problem.
* doc/posix-functions/stat.texi: Mention that this module fixes the
64-bit inode number problem.
* doc/posix-functions/lstat.texi: Likewise.
* doc/posix-functions/fstat.texi: Likewise.
* doc/posix-functions/readdir.texi: Add more details.
* doc/posix-functions/readdir_r.texi: Likewise.
diff --git a/doc/posix-functions/fstat.texi b/doc/posix-functions/fstat.texi
index 579ea42..a404891 100644
--- a/doc/posix-functions/fstat.texi
+++ b/doc/posix-functions/fstat.texi
@@ -16,6 +16,11 @@ On platforms where @code{off_t} is a 32-bit type,
@code{fstat} may not correctly
report the size of files or block devices larger than 2 GB.
(Cf. @code{AC_SYS_LARGEFILE}.)
@item
+On Linux/x86 and Linux/x86_64, applications compiled in 32-bit mode cannot
+access files that happen to have a 64-bit inode number. This can occur with
+file systems such as XFS (typically on large disks) and NFS.
+(Cf. @code{AC_SYS_LARGEFILE}.)
+@item
On Solaris 11.4, when this function yields a timestamp with a
nonpositive @code{tv_sec} value, @code{tv_nsec} might be in the range
@minus{}1000000000..@minus{}1, representing a negative nanoseconds
diff --git a/doc/posix-functions/lstat.texi b/doc/posix-functions/lstat.texi
index 9a03cfb..1b1aff6 100644
--- a/doc/posix-functions/lstat.texi
+++ b/doc/posix-functions/lstat.texi
@@ -13,6 +13,11 @@ On platforms where @code{off_t} is a 32-bit type,
@code{lstat} may not
correctly report the size of files or block devices larger than 2 GB.
(Cf. @code{AC_SYS_LARGEFILE}.)
@item
+On Linux/x86 and Linux/x86_64, applications compiled in 32-bit mode cannot
+access files that happen to have a 64-bit inode number. This can occur with
+file systems such as XFS (typically on large disks) and NFS.
+(Cf. @code{AC_SYS_LARGEFILE}.)
+@item
For symlinks, when the argument ends in a slash, some platforms don't
dereference the argument:
Solaris 9.
diff --git a/doc/posix-functions/readdir.texi b/doc/posix-functions/readdir.texi
index 61ac883..3ec36bd 100644
--- a/doc/posix-functions/readdir.texi
+++ b/doc/posix-functions/readdir.texi
@@ -15,7 +15,8 @@ MSVC 14.
On platforms where @code{off_t} is a 32-bit type, this function may not
work correctly on huge directories larger than 2 GB. Also, on platforms
where @code{ino_t} is a 32-bit type, this function may report inode numbers
-incorrectly. (Cf. @code{AC_SYS_LARGEFILE}.)
+incorrectly. This can occur with file systems such as XFS (typically on
+large disks) and NFS. (Cf. @code{AC_SYS_LARGEFILE}.)
@end itemize
Portability problems not fixed by Gnulib:
diff --git a/doc/posix-functions/readdir_r.texi
b/doc/posix-functions/readdir_r.texi
index a56d390..6153448 100644
--- a/doc/posix-functions/readdir_r.texi
+++ b/doc/posix-functions/readdir_r.texi
@@ -25,5 +25,6 @@ Minix 3.1.8, mingw, MSVC 14.
On platforms where @code{off_t} is a 32-bit type, this function may not
work correctly on huge directories larger than 2 GB. Also, on platforms
where @code{ino_t} is a 32-bit type, this function may report inode numbers
-incorrectly. The fix is to use the @code{AC_SYS_LARGEFILE} macro.
+incorrectly. This can occur with file systems such as XFS (typically on
+large disks) and NFS. The fix is to use the @code{AC_SYS_LARGEFILE} macro.
@end itemize
diff --git a/doc/posix-functions/stat.texi b/doc/posix-functions/stat.texi
index 395717f..27fbe27 100644
--- a/doc/posix-functions/stat.texi
+++ b/doc/posix-functions/stat.texi
@@ -13,6 +13,11 @@ On platforms where @code{off_t} is a 32-bit type,
@code{stat} may not correctly
report the size of files or block devices larger than 2 GB.
(Cf. @code{AC_SYS_LARGEFILE}.)
@item
+On Linux/x86 and Linux/x86_64, applications compiled in 32-bit mode cannot
+access files that happen to have a 64-bit inode number. This can occur with
+file systems such as XFS (typically on large disks) and NFS.
+(Cf. @code{AC_SYS_LARGEFILE}.)
+@item
The @code{st_atime}, @code{st_ctime}, @code{st_mtime} fields are affected by
the current time zone and by the DST flag of the current time zone on some
platforms:
diff --git a/m4/largefile.m4 b/m4/largefile.m4
index 40b16bc..e381339 100644
--- a/m4/largefile.m4
+++ b/m4/largefile.m4
@@ -1,4 +1,5 @@
# Enable large files on systems where this is not the default.
+# Enable support for files on Linux file systems with 64-bit inode numbers.
# Copyright 1992-1996, 1998-2020 Free Software Foundation, Inc.
# This file is free software; the Free Software Foundation
@@ -73,6 +74,9 @@ rm -rf conftest*[]dnl
# one must use special compiler options to get large-file access to work.
# For more details about this brain damage please see:
# http://www.unix.org/version2/whatsnew/lfs20mar.html
+# Additionally, on Linux file systems with 64-bit inodes a file that happens
+# to have a 64-bit inode number cannot be accessed by 32-bit applications on
+# Linux x86/x86_64. This can occur with file systems such as XFS and NFS.
AC_DEFUN([AC_SYS_LARGEFILE],
[AC_ARG_ENABLE(largefile,
[ --disable-largefile omit support for large files])
