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-rw-r--r--make-bcache.c31
1 files changed, 31 insertions, 0 deletions
diff --git a/make-bcache.c b/make-bcache.c
index 6ffe89e..9c038a8 100644
--- a/make-bcache.c
+++ b/make-bcache.c
@@ -269,6 +269,37 @@ static unsigned get_blocksize(const char *path)
exit(EXIT_FAILURE);
}
+ if (S_ISBLK(statbuf.st_mode)) {
+ /* check IO limits:
+ * BLKALIGNOFF: alignment_offset
+ * BLKPBSZGET: physical_block_size
+ * BLKSSZGET: logical_block_size
+ * BLKIOMIN: minimum_io_size
+ * BLKIOOPT: optimal_io_size
+ *
+ * It may be tempting to use physical_block_size,
+ * or even minimum_io_size.
+ * But to be as transparent as possible,
+ * we want to use logical_block_size.
+ */
+ unsigned int logical_block_size;
+ int fd = open(path, O_RDONLY);
+
+ if (fd < 0) {
+ fprintf(stderr, "open(%s) failed: %m\n", path);
+ exit(EXIT_FAILURE);
+ }
+ if (ioctl(fd, BLKSSZGET, &logical_block_size)) {
+ fprintf(stderr, "ioctl(%s, BLKSSZGET) failed: %m\n", path);
+ exit(EXIT_FAILURE);
+ }
+ close(fd);
+ return logical_block_size / 512;
+
+ }
+ /* else: not a block device.
+ * Why would we even want to write a bcache super block there? */
+
return statbuf.st_blksize / 512;
}