Without this patch, the while loop being modified goes on infinitely, but with the patch I am able to boot linux on zfs on a jetson tx2 nx.
It seems like this code was never tested because the logic is clearly wrong. The function do_div(a,b) does a division that modifies the first parameter to have a = a / b, and returns the remainder of the division. So clearly in the usual case when file->offset = 0, the line "blkid = do_div(blkid, blksz);" just results in blkid being set to zero on every iteration of the loop, rather than being incremented as blocks are read. Hence the zeroth block is read over and over and this becomes an infinite loop.
So instead capture the remainder of the division in a "blkoff" variable, and use that to properly calculate the memory address to move from in memmove() below.
For example, if file->offset were 1337, on the first iteration of the loop blkid would be 0 and blkoff would be 1337. If the blksz is 131072 (as it was for me), that amount of data would be copied into data->file_buf. movesize would be 131072 - 1337 = 129735 so 129735 bytes would be moved into buf. On the second iteration of the loop (assuming there is one), red would be 129735, blkid would be 1, blkoff would be 0, and 131072 bytes would be copied into buf. And so on...
Signed-off-by: Phaedrus Leeds mwleeds@mailtundra.com Tested-by: Phaedrus Leeds mwleeds@mailtundra.com --- fs/zfs/zfs.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/fs/zfs/zfs.c b/fs/zfs/zfs.c index 9a50deac18..bfc11fa667 100644 --- a/fs/zfs/zfs.c +++ b/fs/zfs/zfs.c @@ -2128,37 +2128,36 @@ zfs_read(zfs_file_t file, char *buf, uint64_t len) * now, this only reads in one data block at a time. */ length = len; red = 0; while (length) { void *t; /* * Find requested blkid and the offset within that block. */ uint64_t blkid = file->offset + red; - blkid = do_div(blkid, blksz); + uint64_t blkoff = do_div(blkid, blksz); free(data->file_buf); data->file_buf = 0;
err = dmu_read(&(data->dnode), blkid, &t, 0, data); data->file_buf = t; if (err) return -1;
data->file_start = blkid * blksz; data->file_end = data->file_start + blksz;
movesize = min(length, data->file_end - (int)file->offset - red);
- memmove(buf, data->file_buf + file->offset + red - - data->file_start, movesize); + memmove(buf, data->file_buf + blkoff, movesize); buf += movesize; length -= movesize; red += movesize; }
return len; }
int zfs_close(zfs_file_t file)