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39e88ca2c9
When __generic_file_aio_read() hits an error during reading, it reports the
error iff nothing has successfully been read yet. This is condition - when
an error occurs, if nothing has been read/written, report the error code;
otherwise, report the amount of bytes successfully transferred upto that
point.
This corner case can be exposed by performing readv(2) with the following
iov.
iov[0] = len0 @ ptr0
iov[1] = len1 @ NULL (or any other invalid pointer)
iov[2] = len2 @ ptr2
When file size is enough, performing above readv(2) results in
len0 bytes from file_pos @ ptr0
len2 bytes from file_pos + len0 @ ptr2
And the return value is len0 + len2. Test program is attached to this
mail.
This patch makes __generic_file_aio_read()'s error handling identical to
other functions.
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/uio.h>
#include <errno.h>
#include <string.h>
int main(int argc, char **argv)
{
const char *path;
struct stat stbuf;
size_t len0, len1;
void *buf0, *buf1;
struct iovec iov[3];
int fd, i;
ssize_t ret;
if (argc < 2) {
fprintf(stderr, "Usage: testreadv path (better be a "
"small text file)\n");
return 1;
}
path = argv[1];
if (stat(path, &stbuf) < 0) {
perror("stat");
return 1;
}
len0 = stbuf.st_size / 2;
len1 = stbuf.st_size - len0;
if (!len0 || !len1) {
fprintf(stderr, "Dude, file is too small\n");
return 1;
}
if ((fd = open(path, O_RDONLY)) < 0) {
perror("open");
return 1;
}
if (!(buf0 = malloc(len0)) || !(buf1 = malloc(len1))) {
perror("malloc");
return 1;
}
memset(buf0, 0, len0);
memset(buf1, 0, len1);
iov[0].iov_base = buf0;
iov[0].iov_len = len0;
iov[1].iov_base = NULL;
iov[1].iov_len = len1;
iov[2].iov_base = buf1;
iov[2].iov_len = len1;
printf("vector ");
for (i = 0; i < 3; i++)
printf("%p:%zu ", iov[i].iov_base, iov[i].iov_len);
printf("\n");
ret = readv(fd, iov, 3);
if (ret < 0)
perror("readv");
printf("readv returned %zd\nbuf0 = [%s]\nbuf1 = [%s]\n",
ret, (char *)buf0, (char *)buf1);
return 0;
}
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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|---|---|---|
| .. | ||
| bootmem.c | ||
| fadvise.c | ||
| filemap_xip.c | ||
| filemap.c | ||
| filemap.h | ||
| fremap.c | ||
| highmem.c | ||
| hugetlb.c | ||
| internal.h | ||
| Kconfig | ||
| madvise.c | ||
| Makefile | ||
| memory_hotplug.c | ||
| memory.c | ||
| mempolicy.c | ||
| mempool.c | ||
| mincore.c | ||
| mlock.c | ||
| mmap.c | ||
| mprotect.c | ||
| mremap.c | ||
| msync.c | ||
| nommu.c | ||
| oom_kill.c | ||
| page_alloc.c | ||
| page_io.c | ||
| page-writeback.c | ||
| pdflush.c | ||
| prio_tree.c | ||
| readahead.c | ||
| rmap.c | ||
| shmem.c | ||
| slab.c | ||
| sparse.c | ||
| swap_state.c | ||
| swap.c | ||
| swapfile.c | ||
| thrash.c | ||
| tiny-shmem.c | ||
| truncate.c | ||
| vmalloc.c | ||
| vmscan.c | ||