bcachefs: Buffered write path now can avoid the inode lock

Non append, non extending buffered writes can now avoid taking the inode
lock.

To ensure atomicity of writes w.r.t. other writes, we lock every folio
that we'll be writing to, and if this fails we fall back to taking the
inode lock.

Extensive comments are provided as to corner cases.

Link: https://lore.kernel.org/linux-fsdevel/Zdkxfspq3urnrM6I@bombadil.infradead.org/
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: Kill __GFP_NOFAIL in buffered read path

Recently, we fixed our __GFP_NOFAIL usage in the readahead path, but the
easy one in read_single_folio() (where wa can return an error) was
missed - oops.

Fixes:
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: Kill GFP_NOFAIL usage in readahead path

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: darray_for_each() now declares loop iter

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: convert bch_fs_flags to x-macro

Now we can print out filesystem flags in sysfs, useful for debugging
various "what's my filesystem doing" issues.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: allow writeback to fill bio completely

The bcachefs folio writeback code includes a bio full check as well
as a fixed size check to determine when to split off and submit
writeback I/O. The inclusive check of the latter against the limit
means that writeback can submit slightly prematurely. This is not a
functional problem, but results in unnecessarily split I/Os and
extent merging.

This can be observed with a buffered write sized exactly to the
current maximum value (1MB) and with key_merging_disabled=1. The
latter prevents the merge from the second write such that a
subsequent check of the extent list shows a 1020k extent followed by
a contiguous 4k extent.

The purpose for the fixed size check is also undocumented and
somewhat obscure. Lift this check into a new helper that wraps the
bio check, fix the comparison logic, and add a comment to document
the purpose and how we might improve on this in the future.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: Heap allocate btree_trans

We're using more stack than we'd like in a number of functions, and
btree_trans is the biggest object that we stack allocate.

But we have to do a heap allocatation to initialize it anyways, so
there's no real downside to heap allocating the entire thing.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: Fix W=12 build errors

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: Break up io.c

More reorganization, this splits up io.c into
- io_read.c
- io_misc.c - fallocate, fpunch, truncate
- io_write.c

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: Fix swallowing of data in buffered write path

In __bch2_buffered_write, if we fail to write to an entire !uptodate
folio, we have to back out the write, bail out and retry.

But we were missing an iov_iter_revert() call, so the data written to
the folio was lost and the rest of the write shifted to the wrong
offset.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: Split up fs-io.[ch]

fs-io.c is too big - time for some reorganization
- fs-dio.c: direct io
- fs-pagecache.c: pagecache data structures (bch_folio), utility code

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>