On Fri, Sep 29, 2023 at 10:27:07AM +0000, John Garry wrote:
We rely the block layer always being able to send a bio of sizeA bio can have more than BIO_MAX_VECS if you use bio_init.
atomic_write_unit_max without being required to split it due to request
queue or other bio limits.
A bio may contain min(BIO_MAX_VECS, limits->max_segments) vectors,
and each vector is at worst case the device logical block size from
direct IO alignment requirement.
+static unsigned int blk_queue_max_guaranteed_bio_size_sectors(Who is "we", and how tells the caller to only ever use direct I/O?
+ struct request_queue *q)
+{
+ struct queue_limits *limits = &q->limits;
+ unsigned int max_segments = min_t(unsigned int, BIO_MAX_VECS,
+ limits->max_segments);
+ /* Limit according to dev sector size as we only support direct-io */
And how would a type of userspace I/O even matter for low-level
block code.
What if I wanted to use this for file system metadata?