Wire O_DIRECT also to Uncached I/O (#17218)

Before Direct I/O was implemented, I've implemented lighter version
I called Uncached I/O.  It uses normal DMU/ARC data path with some
optimizations, but evicts data from caches as soon as possible and
reasonable.  Originally I wired it only to a primarycache property,
but now completing the integration all the way up to the VFS.

While Direct I/O has the lowest possible memory bandwidth usage,
it also has a significant number of limitations.  It require I/Os
to be page aligned, does not allow speculative prefetch, etc.  The
Uncached I/O does not have those limitations, but instead require
additional memory copy, though still one less than regular cached
I/O.  As such it should fill the gap in between.  Considering this
I've disabled annoying EINVAL errors on misaligned requests, adding
a tunable for those who wants to test their applications.

To pass the information between the layers I had to change a number
of APIs.  But as side effect upper layers can now control not only
the caching, but also speculative prefetch.  I haven't wired it to
VFS yet, since it require looking on some OS specifics.  But while
there I've implemented speculative prefetch of indirect blocks for
Direct I/O, controllable via all the same mechanisms.

Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Fixes #17027
Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>

module/os/linux/zfs/zfs_racct.c

@@ -30,14 +30,14 @@
 #include <linux/task_io_accounting_ops.h>
 
 void
-zfs_racct_read(spa_t *spa, uint64_t size, uint64_t iops, uint32_t flags)
+zfs_racct_read(spa_t *spa, uint64_t size, uint64_t iops, dmu_flags_t flags)
 {
 	task_io_account_read(size);
 	spa_iostats_read_add(spa, size, iops, flags);
 }
 
 void
-zfs_racct_write(spa_t *spa, uint64_t size, uint64_t iops, uint32_t flags)
+zfs_racct_write(spa_t *spa, uint64_t size, uint64_t iops, dmu_flags_t flags)
 {
 	task_io_account_write(size);
 	spa_iostats_write_add(spa, size, iops, flags);
@@ -46,13 +46,13 @@ zfs_racct_write(spa_t *spa, uint64_t size, uint64_t iops, uint32_t flags)
 #else
 
 void
-zfs_racct_read(spa_t *spa, uint64_t size, uint64_t iops, uint32_t flags)
+zfs_racct_read(spa_t *spa, uint64_t size, uint64_t iops, dmu_flags_t flags)
 {
 	(void) spa, (void) size, (void) iops, (void) flags;
 }
 
 void
-zfs_racct_write(spa_t *spa, uint64_t size, uint64_t iops, uint32_t flags)
+zfs_racct_write(spa_t *spa, uint64_t size, uint64_t iops, dmu_flags_t flags)
 {
 	(void) spa, (void) size, (void) iops, (void) flags;
 }

module/os/linux/zfs/zfs_vnops_os.c

@@ -329,7 +329,7 @@ mappedread(znode_t *zp, int nbytes, zfs_uio_t *uio)
 			put_page(pp);
 		} else {
 			error = dmu_read_uio_dbuf(sa_get_db(zp->z_sa_hdl),
-			    uio, bytes);
+			    uio, bytes, DMU_READ_PREFETCH);
 		}
 
 		len -= bytes;

module/os/linux/zfs/zvol_os.c

@@ -258,7 +258,8 @@ zvol_write(zv_request_t *zvr)
 			dmu_tx_abort(tx);
 			break;
 		}
-		error = dmu_write_uio_dnode(zv->zv_dn, &uio, bytes, tx);
+		error = dmu_write_uio_dnode(zv->zv_dn, &uio, bytes, tx,
+		    DMU_READ_PREFETCH);
 		if (error == 0) {
 			zvol_log_write(zv, tx, off, bytes, sync);
 		}
@@ -428,7 +429,8 @@ zvol_read(zv_request_t *zvr)
 		if (bytes > volsize - uio.uio_loffset)
 			bytes = volsize - uio.uio_loffset;
 
-		error = dmu_read_uio_dnode(zv->zv_dn, &uio, bytes);
+		error = dmu_read_uio_dnode(zv->zv_dn, &uio, bytes,
+		    DMU_READ_PREFETCH);
 		if (error) {
 			/* convert checksum errors into IO errors */
 			if (error == ECKSUM)