| Message ID | 1406830068-6485-1-git-send-email-basile@opensource.dyc.edu |
|---|---|
| State | New, archived |
| Headers | show |
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 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
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) {
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(-)