On Thu, Jun 19, 2014 at 11:25:38AM +0800, Qu Wenruo wrote:
Btrfs has global block reservation, so even mkfs.btrfs can execute
without problem, there is still a possibility that the filesystem can't
be mounted.
For example when mkfs.btrfs on a 8M file on x86_64 platform, kernel will
refuse to mount due to ENOSPC, since system block group takes 4M and
mixed block group takes 4M, and global block reservation will takes all
the 4M from mixed block group, which makes btrfs unable to create uuid
tree.
This patch will add minimum device size check before actually mkfs.
The minimum size calculation uses a simplified one:
minimum_size_for_each_dev = 2 * (system block group + global block rsv)
So the global block reserve is set to 1024 * sectorsize. I know the
minimum size guesses are easy to get wrong with various option mixes,
some sane minimum is good. A filesystem in the scale of megabytes is not
recommended anyway.
--- a/mkfs.c
+++ b/mkfs.c
@@ -1337,6 +1337,15 @@ int main(int ac, char **av)
"metadata/data groups\n");
mixed = 1;
}
+ if (block_count < BTRFS_MIN_SIZE_EACH) {
+ fprintf(stderr,
+ "Size '%llu' is too small to make a usable btrfs\n",
+ block_count);
+ fprintf(stderr,
+ "Recommended size for each device is %llu\n",
+ BTRFS_MIN_SIZE_EACH);
I'd suggest to merge the messages into one and do not use "Recommended".
As described in the changelog it's the 'minimum' accepted size.
@@ -1370,6 +1379,21 @@ int main(int ac, char **av)
}
while (dev_cnt-- > 0) {
file = av[optind++];
+ ret = test_minimum_size(file);
+ if (ret < 0) {
+ fprintf(stderr, "Failed to check size for '%s': %s\n",
+ file, strerror(-ret));
+ exit(1);
+ }
+ if (ret > 0) {
+ fprintf(stderr,
+ "'%s' is too small to make a usable btrfs\n",
+ file);
+ fprintf(stderr,
+ "Recommended size for each device is %llu\n",
+ BTRFS_MIN_SIZE_EACH);
+ exit(1);
Same here.
+ }
if (is_block_device(file))
if (test_dev_for_mkfs(file, force_overwrite, estr)) {
fprintf(stderr, "Error: %s", estr);
--- a/utils.h
+++ b/utils.h
@@ -101,5 +101,18 @@ int get_btrfs_mount(const char *dev, char *mp, size_t mp_size);
int find_mount_root(const char *path, char **mount_root);
int get_device_info(int fd, u64 devid,
struct btrfs_ioctl_dev_info_args *di_args);
+int test_minimum_size(const char *file);
+/*
+ * Btrfs minimum size calculation is complicated, it should include at least:
+ * 1. system group size
+ * 2. minimum global block reserve
+ * 3. metadata used at mkfs
+ * 4. space reservation to create uuid for first mount.
+ * Also, raid factor should also be taken into consideration.
+ * To avoid the overkill calculation, (system group + global block rsv) * 2
+ * for *EACH* device should be good enough.
+ */
+#define BTRFS_MIN_SIZE_EACH (2 * (BTRFS_MKFS_SYSTEM_GROUP_SIZE + \
+ ((u64)sysconf(_SC_PAGESIZE) << 10)))
The use of PAGESIZE here is well hidden in the macro, although it should
be sectorsize of the currently created filesystem. Also,
BTRFS_MIN_SIZE_EACH should be rather denote it's related to a device, so
BTRFS_MIN_DEVICE_SIZE.
Separating the minimum global block reserve size into a macro would be
also cleaner.
Thanks.
