Messages in this thread | | | Date | Fri, 11 Jun 2010 13:05:32 +0800 | From | Tao Ma <> | Subject | Re: fiemap is broken for sparse file in ext4? |
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Hi Eric, Thanks for the quick response.
On 06/11/2010 12:08 PM, Eric Sandeen wrote: > Tao Ma wrote: >> Hi Ted and other ext4 gurus, >> I found fiemap may be broken for sparse files in ext4. Here is a >> simple example. >> >> dd if=/dev/zero of=testfile1 bs=1M count=1 >> using fiemap shows that it has a delalloc extent. >> Logical: 0 Ext length: 1048576 Physical: 0 flags: 7 >> >> flags 7 means FIEMAP_EXTENT_LAST, FIEMAP_EXTENT_UNKNOWN and >> FIEMAP_EXTENT_DELALLOC, >> >> while if we create a sparse file, fiemap will not show the delalloc extent. >> dd if=/dev/zero of=testfile1 bs=1M count=1 seek=1 >> using fiemap shows that it has no extent for the file. while we should >> have some output like: >> Logical: 1048576 Ext length: 1048576 Physical: 0 flags: 7 >> >> So we have different output with sparse and non-sparse file. Is it a bug >> for ext4? > > What are you using to call fiemap? Here it seems to be working: I just wrote a simple test program by calling ioctl. It is attached. btw, you need to call it immediately after dd so that we have a chance that ext4 don't have time to allocate extents. ;) > > # dd if=/dev/zero of=testfile1 bs=1M count=1 seek=1; > > # filefrag -v testfile1 > Filesystem type is: ef53 > Filesystem cylinder groups is approximately 119 > File size of testfile1 is 2097152 (512 blocks, blocksize 4096) > ext logical physical expected length flags > 0 256 151946 1 merged > 1 257 151951 151946 2 merged > 2 259 152434 151952 253 merged,eof > testfile1: 4 extents found I guess maybe filefrag use the diffrent ioctl flag, maybe FIEMAP_FLAG_SYNC to let ext4 sync first.
Regards, Tao #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <errno.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <sys/ioctl.h> #include <stdint.h> #include <inttypes.h> #include <string.h>
#include "fiemap.h"
#define FS_IOC_FIEMAP _IOWR('f', 11, struct fiemap)
static unsigned int num_extents = 1024; static unsigned int estimate_extents = 1;
static unsigned long long map_start = 0ULL; static unsigned long long map_len = FIEMAP_MAX_OFFSET; static char *fname; static unsigned int blocksize = 4096;
static void usage(void) { printf("Usage: fiemap filename\n"); exit(1); }
static void print_extent(struct fiemap_extent *extent) { __u64 val;
printf("Logical: ###[%8"PRIu64"]\t", extent->fe_logical); printf("Ext length: ###[%8"PRIu64"]\t", extent->fe_length); printf("Physical: ###[%8"PRIu64"]\t", extent->fe_physical); printf("flags: %u\t", extent->fe_flags);
if (extent->fe_flags & FIEMAP_EXTENT_SHARED) printf("Yeah, found an shared extent\n"); if (extent->fe_flags & FIEMAP_EXTENT_UNWRITTEN) printf("Yeah, you are hole?\n");
printf("\n"); }
static void show_results(struct fiemap *fiemap) { int i;
printf("Extents returned: %u\n", fiemap->fm_mapped_extents); if (fiemap->fm_extent_count == 0 || fiemap->fm_mapped_extents == 0) return;
for (i = 0; i < fiemap->fm_mapped_extents; i++) print_extent(&fiemap->fm_extents[i]);
}
static int figure_extents(int fd, unsigned int *num) { int ret; struct fiemap fiemap = { 0, };
fiemap.fm_start = map_start; fiemap.fm_length = map_len; fiemap.fm_flags = 0;
ret = ioctl(fd, FS_IOC_FIEMAP, &fiemap); if (ret == -1) { fprintf(stderr, "fiemap get count error %d: \"%s\"\n", errno, strerror(errno)); return -1; }
*num = fiemap.fm_mapped_extents;
return 0; }
int main(int argc, char **argv) { int ret, fd; struct fiemap *fiemap;
fd = open(argv[1], O_RDONLY); if (fd == -1) { fprintf(stderr, "open error %d: \"%s\"\n", errno, strerror(errno)); return -1; }
if (figure_extents(fd, &num_extents)) return -1;
printf("Extents in file \"%s\": %u\n", argv[1], num_extents);
fiemap = malloc(sizeof(fiemap) + num_extents * sizeof(struct fiemap_extent)); if (fiemap == NULL) { fprintf(stderr, "malloc error %d: \"%s\"\n", errno, strerror(errno)); return -1; }
fiemap->fm_start = map_start; fiemap->fm_length = map_len; fiemap->fm_extent_count = num_extents;
ret = ioctl(fd, FS_IOC_FIEMAP, fiemap); if (ret == -1) { if (errno == EBADR) { fprintf(stderr, "Kernel does not support the flags: 0x%x\n", fiemap->fm_flags); return -1; } fprintf(stderr, "fiemap error %d: \"%s\"\n", errno, strerror(errno)); return -1; }
show_results(fiemap);
close(fd);
return 0; }
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