On 2018/6/20 5:51 PM, Arnd Bergmann wrote: > bcache uses get_seconds() to read the current system time and store it in > the superblock as well as in uuid_entry structures that are user visible. > > This changes over from the deprecated function to > ktime_get_real_seconds(), which returns a 64-bit timestamp as it > should. Unfortunately, the two structures are still limited to 32 bits, > so this won't fix any real problems. Let's at least document that > properly, in case we get an updated format in the future it can be > fixed. Until then, we still have some time, and checking the tools > at https://github.com/koverstreet/bcache-tools reveals no access to > any of them. > > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> Hi Arnd, Firstly thanks to your patch, especially the detailed information in patch log, it helps me to understand the problem more easier. >From the information, it seems the problem is current 32bit time stamp will be overflow in 2106. So it will be 88 years later, which I have to say I don't care. Also for get_seconds() which works well for current code as many other places call it, I would like to keep it. But the code comments in bcache.h looks good, if you want to send a single patch for the code comments for bcache.h, I would like to see it. Thanks. Coly Li > --- > drivers/md/bcache/super.c | 23 +++++++++++++++++------ > include/uapi/linux/bcache.h | 4 ++-- > 2 files changed, 19 insertions(+), 8 deletions(-) > > diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c > index fa4058e43202..aa9790ee5cb5 100644 > --- a/drivers/md/bcache/super.c > +++ b/drivers/md/bcache/super.c > @@ -53,6 +53,17 @@ struct workqueue_struct *bcache_wq; > /* limitation of bcache devices number on single system */ > #define BCACHE_DEVICE_IDX_MAX ((1U << MINORBITS)/BCACHE_MINORS) > > +/* > + * various timestamp fields in the superblock are unfortunately > + * limited to 32 bits, which will lead to overflow in year 2106. > + * > + * If we ever get a new superblock format, that should be fixed. > + */ > +static inline u32 bcache_get_realtime32(void) > +{ > + return (u32)ktime_get_real_seconds(); > +} > + > /* Superblock */ > > static const char *read_super(struct cache_sb *sb, struct block_device *bdev, > @@ -181,7 +192,7 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev, > goto err; > } > > - sb->last_mount = get_seconds(); > + sb->last_mount = bcache_get_realtime32(); > err = NULL; > > get_page(bh->b_page); > @@ -701,7 +712,7 @@ static void bcache_device_detach(struct bcache_device *d) > > SET_UUID_FLASH_ONLY(u, 0); > memcpy(u->uuid, invalid_uuid, 16); > - u->invalidated = cpu_to_le32(get_seconds()); > + u->invalidated = cpu_to_le32(bcache_get_realtime32()); > bch_uuid_write(d->c); > } > > @@ -1027,7 +1038,7 @@ void bch_cached_dev_detach(struct cached_dev *dc) > int bch_cached_dev_attach(struct cached_dev *dc, struct cache_set *c, > uint8_t *set_uuid) > { > - uint32_t rtime = cpu_to_le32(get_seconds()); > + uint32_t rtime = cpu_to_le32(bcache_get_realtime32()); > struct uuid_entry *u; > struct cached_dev *exist_dc, *t; > > @@ -1070,7 +1081,7 @@ int bch_cached_dev_attach(struct cached_dev *dc, struct cache_set *c, > (BDEV_STATE(&dc->sb) == BDEV_STATE_STALE || > BDEV_STATE(&dc->sb) == BDEV_STATE_NONE)) { > memcpy(u->uuid, invalid_uuid, 16); > - u->invalidated = cpu_to_le32(get_seconds()); > + u->invalidated = cpu_to_le32(bcache_get_realtime32()); > u = NULL; > } > > @@ -1390,7 +1401,7 @@ int bch_flash_dev_create(struct cache_set *c, uint64_t size) > > get_random_bytes(u->uuid, 16); > memset(u->label, 0, 32); > - u->first_reg = u->last_reg = cpu_to_le32(get_seconds()); > + u->first_reg = u->last_reg = cpu_to_le32(bcache_get_realtime32()); > > SET_UUID_FLASH_ONLY(u, 1); > u->sectors = size >> 9; > @@ -1894,7 +1905,7 @@ static void run_cache_set(struct cache_set *c) > goto err; > > closure_sync(&cl); > - c->sb.last_mount = get_seconds(); > + c->sb.last_mount = bcache_get_realtime32(); > bcache_write_super(c); > > list_for_each_entry_safe(dc, t, &uncached_devices, list) > diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h > index 821f71a2e48f..8d19e02d752a 100644 > --- a/include/uapi/linux/bcache.h > +++ b/include/uapi/linux/bcache.h > @@ -195,7 +195,7 @@ struct cache_sb { > }; > }; > > - __u32 last_mount; /* time_t */ > + __u32 last_mount; /* time overflow in y2106 */ > > __u16 first_bucket; > union { > @@ -318,7 +318,7 @@ struct uuid_entry { > struct { > __u8 uuid[16]; > __u8 label[32]; > - __u32 first_reg; > + __u32 first_reg; /* time overflow in y2106 */ > __u32 last_reg; > __u32 invalidated; > > -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
