[PATCH] misc/e4defrag.c: use posix_fallocate64() if fallocate64() is unavailable

[PATCH] misc/e4defrag.c: use posix_fallocate64() if fallocate64() is unavailable

[basile]

From: "Anthony G. Basile" <blueness@gentoo.org>

Commit 58229aaf removed the broken fallback syscall for fallocate64() on systems
where the latter is unavailable.  However, it did not provide a substitute,
so the build fails on uClibc which does not have fallocate64(), but does have
posix_fallocate64().  Since fallocate64() is called with mode=0, we can make use
of posix_fallocate64() on such systems.

See `man 2 fallocate` and `man 3 posix_fallocate`.
---
 configure       |  2 +-
 configure.in    |  1 +
 lib/config.h.in |  3 +++
 misc/e4defrag.c | 10 +++++++---
 4 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/configure b/configure
index 6c503aa..9853bc0 100755
--- a/configure
+++ b/configure
@@ -13071,7 +13071,7 @@ if test "$ac_res" != no; then :
 fi
 
 fi
-for ac_func in  	__secure_getenv 	backtrace 	blkid_probe_get_topology 	blkid_probe_enable_partitions 	chflags 	fadvise64 	fallocate 	fallocate64 	fchown 	fdatasync 	fstat64 	ftruncate64 	futimes 	getcwd 	getdtablesize 	getmntinfo 	getpwuid_r 	getrlimit 	getrusage 	jrand48 	llistxattr 	llseek 	lseek64 	mallinfo 	mbstowcs 	memalign 	mempcpy 	mmap 	msync 	nanosleep 	open64 	pathconf 	posix_fadvise 	posix_fadvise64 	posix_memalign 	prctl 	secure_getenv 	setmntent 	setresgid 	setresuid 	snprintf 	srandom 	stpcpy 	strcasecmp 	strdup 	strnlen 	strptime 	strtoull 	sync_file_range 	sysconf 	usleep 	utime 	valloc
+for ac_func in  	__secure_getenv 	backtrace 	blkid_probe_get_topology 	blkid_probe_enable_partitions 	chflags 	fadvise64 	fallocate 	fallocate64 	fchown 	fdatasync 	fstat64 	ftruncate64 	futimes 	getcwd 	getdtablesize 	getmntinfo 	getpwuid_r 	getrlimit 	getrusage 	jrand48 	llistxattr 	llseek 	lseek64 	mallinfo 	mbstowcs 	memalign 	mempcpy 	mmap 	msync 	nanosleep 	open64 	pathconf 	posix_fadvise 	posix_fadvise64 	posix_fallocate64 	posix_memalign 	prctl 	secure_getenv 	setmntent 	setresgid 	setresuid 	snprintf 	srandom 	stpcpy 	strcasecmp 	strdup 	strnlen 	strptime 	strtoull 	sync_file_range 	sysconf 	usleep 	utime 	valloc
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
diff --git a/configure.in b/configure.in
index 67e5453..48fa099 100644
--- a/configure.in
+++ b/configure.in
@@ -1113,6 +1113,7 @@ AC_CHECK_FUNCS(m4_flatten([
 	pathconf
 	posix_fadvise
 	posix_fadvise64
+	posix_fallocate64
 	posix_memalign
 	prctl
 	secure_getenv
diff --git a/lib/config.h.in b/lib/config.h.in
index 12a609a..3d6796d 100644
--- a/lib/config.h.in
+++ b/lib/config.h.in
@@ -331,6 +331,9 @@
 /* Define to 1 if you have the `posix_fadvise64' function. */
 #undef HAVE_POSIX_FADVISE64
 
+/* Define to 1 if you have the `posix_fallocate64' function. */
+#undef HAVE_POSIX_FALLOCATE64
+
 /* Define to 1 if you have the `posix_memalign' function. */
 #undef HAVE_POSIX_MEMALIGN
 
diff --git a/misc/e4defrag.c b/misc/e4defrag.c
index d0eac60..ba16a76 100644
--- a/misc/e4defrag.c
+++ b/misc/e4defrag.c
@@ -197,9 +197,9 @@ static struct frag_statistic_ino	frag_rank[SHOW_FRAG_FILES];
 #error sync_file_range not available!
 #endif /* ! HAVE_SYNC_FILE_RANGE */
 
-#ifndef HAVE_FALLOCATE64
-#error fallocate64 not available!
-#endif /* ! HAVE_FALLOCATE64 */
+#if !defined(HAVE_FALLOCATE64) && !defined(HAVE_POSIX_FALLOCATE64)
+#error neither fallocate64 nor posix_fallocate64 available!
+#endif /* ! HAVE_FALLOCATE64 && ! HAVE_POSIX_FALLOCATE64 */
 
 /*
  * get_mount_point() -	Get device's mount point.
@@ -1554,7 +1554,11 @@ static int file_defrag(const char *file, const struct stat64 *buf,
 	/* Allocate space for donor inode */
 	orig_group_tmp = orig_group_head;
 	do {
+#ifdef HAVE_FALLOCATE64
 		ret = fallocate64(donor_fd, 0,
+#else /* HAVE_POSIX_FALLOCATE64 */
+		ret = posix_fallocate64(donor_fd,
+#endif
 		  (loff_t)orig_group_tmp->start->data.logical * block_size,
 		  (loff_t)orig_group_tmp->len * block_size);
 		if (ret < 0) {
-- 
1.8.5.5

Re: [PATCH] misc/e4defrag.c: use posix_fallocate64() if fallocate64() is unavailable

[Theodore Ts'o]

On Thu, Jul 31, 2014 at 02:07:48PM -0400, basile@opensource.dyc.edu wrote:
> From: "Anthony G. Basile" <blueness@gentoo.org>
> 
> Commit 58229aaf removed the broken fallback syscall for fallocate64() on systems
> where the latter is unavailable.  However, it did not provide a substitute,
> so the build fails on uClibc which does not have fallocate64(), but does have
> posix_fallocate64().  Since fallocate64() is called with mode=0, we can make use
> of posix_fallocate64() on such systems.

The posix_fallocate[64]() is not the same as fallocate[64]().  Some
libc's will implement posix_fallocate() by brute force writing zeros
to the file.  Some will try calling the fallocate(2) system call if it
is present, and then fall back to the brute force write.  With
fallocate(2), if the file system returns ENOTSUPP, userspace gets told
about it.

So one question is how has uClibc actually implemented with
posix_fallocate[64]()?  Does it implement fallocate()?  I'd be happier
falling back to fallocate() and simply failing to support files which
are larger than the maximum size supported by off_t.

Yet another possibility is simply changing the Makefile to simply skip
building e4defrag if the C library doesn't support the fallocate
system call.

						- Ted

Re: [PATCH] misc/e4defrag.c: use posix_fallocate64() if fallocate64() is unavailable

[Anthony G. Basile]

On 07/31/14 19:22, Theodore Ts'o wrote:
> On Thu, Jul 31, 2014 at 02:07:48PM -0400, basile@opensource.dyc.edu wrote:
>> From: "Anthony G. Basile" <blueness@gentoo.org>
>>
>> Commit 58229aaf removed the broken fallback syscall for fallocate64() on systems
>> where the latter is unavailable.  However, it did not provide a substitute,
>> so the build fails on uClibc which does not have fallocate64(), but does have
>> posix_fallocate64().  Since fallocate64() is called with mode=0, we can make use
>> of posix_fallocate64() on such systems.
>
> The posix_fallocate[64]() is not the same as fallocate[64]().  Some
> libc's will implement posix_fallocate() by brute force writing zeros
> to the file.  Some will try calling the fallocate(2) system call if it
> is present, and then fall back to the brute force write.  With
> fallocate(2), if the file system returns ENOTSUPP, userspace gets told
> about it.
>
> So one question is how has uClibc actually implemented with
> posix_fallocate[64]()?  Does it implement fallocate()?  I'd be happier
> falling back to fallocate() and simply failing to support files which
> are larger than the maximum size supported by off_t.

Sorry for the dealy in responding.  uclibc does implement 
posix_fallocate using the fallocate syscall and it does report ENOTSUPP. 
[1] This is basically the way e4defrag.c was doing things before 
58229aaf, but without the problem that was there.  What does concern me 
if there are *other* libc's that try to brute force zero.  I could 
update the patch to check ifdef __UCLIBC__ since we know that 
implementation is safe.  Thoughts?

[1] See 
http://git.uclibc.org/uClibc/tree/libc/sysdeps/linux/common/posix_fallocate.c 
and posix_fallocate64.c

>
> Yet another possibility is simply changing the Makefile to simply skip
> building e4defrag if the C library doesn't support the fallocate
> system call.

I think we can do this if its not uclibc.  I don't know of any libc 
which does the brute forcing, but I'm only familiar with glibc, uclibc 
and musl, and only the linux kernel.  Both glibc and musl provide 
fallocate(2).  Only uclibc doesn't.  Maybe its time to implement it in 
uclibc.

>
> 						- Ted
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-- 
Anthony G. Basile, Ph. D.
Chair of Information Technology
D'Youville College
Buffalo, NY 14201
(716) 829-8197