On Tue, Sep 14, 2021 at 11:14 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> All this pain could have been trivially avoided with just people
> writing better code, knowing that multiplies and divides are
> expensive, and that shift counts are small and cheap.
IOW, maybe the fix is just this attached trivial patch.
I didn't bother to change the order of the 'struct ndb_config'
structure. It would pack better if you put the (now 32-bit)
blksize_bits field next to the 'atomic_t' field, I think. But I wanted
to just see how a minimal patch looks.
I did make the debugfs interface reflect the change to blocksize_bits,
so this is visible in user space. But it's debugfs.
If people care, it could be made to use a DEFINE_SHOW_ATTRIBUTE()
function the way it already does for 'flags', so that's not a
fundamental issue, I just didn't bother.
Hmm?
Btw, I really think more of the block layer should perhaps think about
use bit shifts more, not expanded values. Can things like the queue
'discard_alignment' really be non-powers-of-two?
Linus
drivers/block/nbd.c | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 5170a630778d..9e12edf892d7 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -97,13 +97,18 @@ struct nbd_config {
atomic_t recv_threads;
wait_queue_head_t recv_wq;
- loff_t blksize;
+ unsigned blksize_bits;
loff_t bytesize;
#if IS_ENABLED(CONFIG_DEBUG_FS)
struct dentry *dbg_dir;
#endif
};
+static inline unsigned int nbd_blksize(struct nbd_config *config)
+{
+ return 1u << config->blksize_bits;
+}
+
struct nbd_device {
struct blk_mq_tag_set tag_set;
@@ -146,7 +151,7 @@ static struct dentry *nbd_dbg_dir;
#define NBD_MAGIC 0x68797548
-#define NBD_DEF_BLKSIZE 1024
+#define NBD_DEF_BLKSIZE_BITS 10
static unsigned int nbds_max = 16;
static int max_part = 16;
@@ -317,12 +322,12 @@ static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize,
loff_t blksize)
{
if (!blksize)
- blksize = NBD_DEF_BLKSIZE;
+ blksize = 1u << NBD_DEF_BLKSIZE_BITS;
if (blksize < 512 || blksize > PAGE_SIZE || !is_power_of_2(blksize))
return -EINVAL;
nbd->config->bytesize = bytesize;
- nbd->config->blksize = blksize;
+ nbd->config->blksize_bits = __ffs(blksize);
if (!nbd->task_recv)
return 0;
@@ -1337,7 +1342,7 @@ static int nbd_start_device(struct nbd_device *nbd)
args->index = i;
queue_work(nbd->recv_workq, &args->work);
}
- return nbd_set_size(nbd, config->bytesize, config->blksize);
+ return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
}
static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *bdev)
@@ -1406,11 +1411,12 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
case NBD_SET_BLKSIZE:
return nbd_set_size(nbd, config->bytesize, arg);
case NBD_SET_SIZE:
- return nbd_set_size(nbd, arg, config->blksize);
+ return nbd_set_size(nbd, arg, nbd_blksize(config));
case NBD_SET_SIZE_BLOCKS:
- if (check_mul_overflow((loff_t)arg, config->blksize, &bytesize))
+ bytesize = arg << config->blksize_bits;
+ if (bytesize >> config->blksize_bits != arg)
return -EINVAL;
- return nbd_set_size(nbd, bytesize, config->blksize);
+ return nbd_set_size(nbd, bytesize, nbd_blksize(config));
case NBD_SET_TIMEOUT:
nbd_set_cmd_timeout(nbd, arg);
return 0;
@@ -1476,7 +1482,7 @@ static struct nbd_config *nbd_alloc_config(void)
atomic_set(&config->recv_threads, 0);
init_waitqueue_head(&config->recv_wq);
init_waitqueue_head(&config->conn_wait);
- config->blksize = NBD_DEF_BLKSIZE;
+ config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
atomic_set(&config->live_connections, 0);
try_module_get(THIS_MODULE);
return config;
@@ -1604,7 +1610,7 @@ static int nbd_dev_dbg_init(struct nbd_device *nbd)
debugfs_create_file("tasks", 0444, dir, nbd, &nbd_dbg_tasks_fops);
debugfs_create_u64("size_bytes", 0444, dir, &config->bytesize);
debugfs_create_u32("timeout", 0444, dir, &nbd->tag_set.timeout);
- debugfs_create_u64("blocksize", 0444, dir, &config->blksize);
+ debugfs_create_u32("blocksize_bits", 0444, dir, &config->blksize_bits);
debugfs_create_file("flags", 0444, dir, nbd, &nbd_dbg_flags_fops);
return 0;
@@ -1826,7 +1832,7 @@ nbd_device_policy[NBD_DEVICE_ATTR_MAX + 1] = {
static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
{
struct nbd_config *config = nbd->config;
- u64 bsize = config->blksize;
+ u64 bsize = nbd_blksize(config);
u64 bytes = config->bytesize;
if (info->attrs[NBD_ATTR_SIZE_BYTES])
@@ -1835,7 +1841,7 @@ static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES])
bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);
- if (bytes != config->bytesize || bsize != config->blksize)
+ if (bytes != config->bytesize || bsize != nbd_blksize(config))
return nbd_set_size(nbd, bytes, bsize);
return 0;
}
