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Subject[PATCH 0/6][TAKE7] fallocate system call
This is the latest fallocate patchset and is based on 2.6.22.

* Following are the changes from TAKE6:
1) We now just have two modes (and no deallocation modes).
2) Updated the man page
3) Added a new patch submitted by David P. Quigley (Patch 3/6).
4) Used EXT_INIT_MAX_LEN instead of 0x8000 in Patch 6/6.
5) Included below in the end is a small testcase to test fallocate.

* Following are the changes from TAKE5 to TAKE6:
1) Rebased to 2.6.22
2) Added compat wrapper for x86_64
3) Dropped s390 and ia64 patches, since the platform maintaners can
add the support for fallocate once it is in mainline.
4) Added a change suggested by Andreas for better extent-to-group
alignment in ext4 (Patch 6/6). Please refer following post:
5) Renamed mode flags and values from "FA_" to "FALLOC_"
6) Added manpage (updated version of the one initially submitted by
David Chinner).

1> Implementation on other architectures (other than i386, x86_64,
and ppc64). s390(x) and ia64 patches are ready and will be pushed
by platform maintaners when the fallocate is in mainline.
2> A generic file system operation to handle fallocate
(generic_fallocate), for filesystems that do _not_ have the fallocate
inode operation implemented.
3> Changes to glibc,
a) to support fallocate() system call
b) to make posix_fallocate() and posix_fallocate64() call fallocate()
4> Patch to e2fsprogs to recognize and display uninitialized extents.

Following patches follow:
Patch 1/6 : manpage for fallocate
Patch 2/6 : fallocate() implementation in i386, x86_64 and powerpc
Patch 3/6 : revalidate write permissions for fallocate
Patch 4/6 : ext4: fallocate support in ext4
Patch 5/6 : ext4: write support for preallocated blocks
Patch 6/6 : ext4: change for better extent-to-group alignment

Note: Attached below is a small testcase to test fallocate. The __NR_fallocate
will need to be changed depending on the system call number in the kernel (it
may get changed due to merge) and also depending on the architecture.

Amit Arora

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>

#include <linux/unistd.h>
#include <sys/vfs.h>
#include <sys/stat.h>

#define VERBOSE 0

#define __NR_fallocate 324

#define FALLOC_FL_KEEP_SIZE 0x01

int do_fallocate(int fd, int mode, loff_t offset, loff_t len)
int ret;

printf("Trying to preallocate blocks (offset=%llu, len=%llu)\n",
offset, len);
ret = syscall(__NR_fallocate, fd, mode, offset, len);

if (ret <0) {
printf("SYSCALL: received error %d, ret=%d\n", errno, ret);

printf("fallocate system call succedded ! ret=%d\n", ret);

return ret;

int test_fallocate(int fd, int mode, loff_t offset, loff_t len)
int ret, blocks;
struct stat statbuf1, statbuf2;

fstat(fd, &statbuf1);

ret = do_fallocate(fd, mode, offset, len);

fstat(fd, &statbuf2);

/* check file size after preallocation */
if (mode == FALLOC_ALLOCATE) {
if (!ret && statbuf1.st_size < (offset + len) &&
statbuf2.st_size != (offset + len)) {
printf("Error: fallocate succeeded, but the file size did not "
"change, where it should have!\n");
ret = 1;
} else if (statbuf1.st_size != statbuf2.st_size) {
printf("Error : File size changed, when it should not have!\n");
ret = 1;

blocks = ((statbuf2.st_blocks - statbuf1.st_blocks) * 512)/ statbuf2.st_blksize;

/* Print report */
printf("# FALLOCATE TEST REPORT #\n");
printf("\tNew blocks preallocated = %d.\n", blocks);
printf("\tNumber of bytes preallocated = %d\n", blocks * statbuf2.st_blksize);
printf("\tOld file size = %d, New file size %d.\n",
statbuf1.st_size, statbuf2.st_size);
printf("\tOld num blocks = %d, New num blocks %d.\n",
(statbuf1.st_blocks * 512)/1024, (statbuf2.st_blocks * 512)/1024);

return ret;

int do_write(int fd, loff_t offset, loff_t len)
int ret;
char *buf;

buf = (char *)malloc(len);
if (!buf) {
printf("error: malloc failed.\n");

printf("Trying to write to file (offset=%llu, len=%llu)\n",
offset, len);

ret = lseek(fd, offset, SEEK_SET);
if (ret != offset) {
printf("lseek() failed error=%d, ret=%d\n", errno, ret);

ret = write(fd, buf, len);
if (ret != len) {
printf("write() failed error=%d, ret=%d\n", errno, ret);

printf("Write succedded ! Written %llu bytes ret=%d\n", len, ret);

return ret;

int test_write(int fd, loff_t offset, loff_t len)
int ret;

ret = do_write(fd, offset, len);
printf("# WRITE TEST REPORT #\n");
if (ret > 0) printf("\t written %d bytes.\n", ret);
else printf("\t write operation failed!\n");

if (ret > 0) return 0;
else return 1;

void usage(char **argv)
printf("\n%s <option> <filename-with-path> <offset> <length>\n", argv[0]);
printf("option can be one of the following :\n");
printf("\t-f\t: preallocate. This maps to FALLOC_ALLOCATE mode.\n");
printf("\t-F\t: preallocate, but do not change the file size.\n");
printf("\t\t This maps to FALLOC_RESV_SPACE mode.\n");
printf("\t-w\t: write some data to the range.\n");
printf("\t-W\t: preallocate and write some data to the range.\n");

* Arguments:
* argv[1] = option (-f/-F/-w/-W/-m)
* argv[2] = fname : the file name with path
* argv[3] = offset : in bytes
* argv[4] = len : in bytes
int main(int argc, char **argv)
int ret = 1, fd, mode;
char *fname;
loff_t offset, len;

if (argc!=5 || argv[1][0] != '-') {

fname = argv[2];
offset = (unsigned long long)atol(argv[3]);;
len = (unsigned long long)atol(argv[4]);

if (offset < 0 || len <= 0) {
printf("%s: Invalid arguments.\n", argv[0]);

fd = open(fname, O_CREAT|O_RDWR, 0666);
if (fd < 0) {
printf("Error opening file %s, error = %d.\n", fname, errno);

/* -f */
if (!strcmp(argv[1], "-f")) {
ret = test_fallocate(fd, mode, offset, len);
if (ret) printf("test_fallocate: ERROR ! ret=%d\n", ret);
/* -F */
} else if (!strcmp(argv[1], "-F")) {
ret = test_fallocate(fd, mode, offset, len);
if (ret) printf("test_fallocate: ERROR ! ret=%d\n", ret);
/* -w */
} else if (!strcmp(argv[1], "-w")) {
ret = test_write(fd, offset, len);
/* -W */
} else if (!strcmp(argv[1], "-W")) {
ret = test_fallocate(fd, mode, offset, len);
if (ret) {
printf("test_fallocate: ERROR ! ret=%d\n", ret);
goto out;
ret = test_write(fd, offset, len);
if (ret) printf("test_write: ERROR ! ret=%d\n", ret);
} else {
printf("%s: Invalid arguments.\n", argv[0]);


if (!ret) printf("\n\n### TESTS PASSED ###\n");
else printf("\n\n#!# TESTS FAILED #!#\n");

return ret;
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