Kernel compatibility changes for iomap on EL8

Add KC_USE_IOMAP_FOR_IO and only build the iomap R/W pieces
for EL9 and higher. We support iomap for fiemap and llseek
on EL8.

Signed-off-by: Chris Kirby <ckirby@versity.com>

kmod/src/Makefile.kernelcompat

@@ -222,3 +222,13 @@ endif
 ifneq (,$(shell grep 'define timer_container_of' include/linux/timer.h))
 ccflags-y += -DKC_TIMER_CONTAINER_OF
 endif
+
+#
+# v6.4-rc1-4f80818b4a58c
+#
+# iomap needs iterator nofault support in the read/write paths. We can still
+# use iomap for fiemap and llseek though.
+#
+ifneq (,$(shell grep 'copy_page_to_iter_nofault' include/linux/uio.h))
+ccflags-y += -DKC_USE_IOMAP_FOR_IO
+endif

kmod/src/data.c

@@ -1173,6 +1173,7 @@ out:
 	return ret;
 }
 
+#ifdef KC_USE_IOMAP_FOR_IO
 static int scoutfs_fadvise(struct file *file, loff_t start, loff_t end, int advice)
 {
 	struct inode *inode = file_inode(file);
@@ -1203,6 +1204,7 @@ static int scoutfs_fadvise(struct file *file, loff_t start, loff_t end, int advi
 
 	return ret;
 }
+#endif
 
 /*
  * A special case of initializing a single large offline extent.  This
@@ -2122,7 +2124,9 @@ static vm_fault_t scoutfs_data_filemap_fault(struct vm_fault *vmf)
 	loff_t pos;
 	int err;
 	vm_fault_t ret = VM_FAULT_SIGBUS;
+#ifdef KC_USE_IOMAP_FOR_IO
 	void *semlock;
+#endif
 	bool found_lock;
 
 	pos = vmf->pgoff;
@@ -2157,19 +2161,23 @@ retry:
 		found_lock = true;
 	}
 
+#ifdef KC_USE_IOMAP_FOR_IO
 	semlock = scoutfs_per_task_get(&si->pt_extent_sem);
 	if (semlock == NULL) {
 		down_read(&si->extent_sem);
 		if (!scoutfs_per_task_add_excl(&si->pt_extent_sem, &pt_sem, &semlock))
 			WARN_ON_ONCE(true);
 	}
+#endif
 
 	ret = filemap_fault(vmf);
 
+#ifdef KC_USE_IOMAP_FOR_IO
 	if (semlock == NULL) {
 		up_read(&si->extent_sem);
 		scoutfs_per_task_del(&si->pt_extent_sem, &pt_sem);
 	}
+#endif
 
 out:
 	if (!found_lock) {
@@ -2232,7 +2240,9 @@ const struct file_operations scoutfs_file_fops = {
 	.fsync		= scoutfs_file_fsync,
 	.llseek		= scoutfs_file_llseek,
 	.fallocate	= scoutfs_fallocate,
+#ifdef KC_USE_IOMAP_FOR_IO
 	.fadvise	= scoutfs_fadvise,
+#endif
 };
 
 void scoutfs_data_init_btrees(struct super_block *sb,

kmod/src/file.c

@@ -34,6 +34,8 @@
 #include "trans.h"
 #include "msg.h"
 
+#ifdef KC_USE_IOMAP_FOR_IO
+
 static int lock_for_iomap_read(struct inode *inode, bool nowait,
 			       struct scoutfs_per_task_entry *pt_extent_ent)
 {
@@ -61,7 +63,6 @@ static void unlock_for_iomap_read(struct inode *inode,
 	up_read(&si->extent_sem);
 }
 
-#ifdef KC_USE_IOMAP_FOR_IO
 static bool scoutfs_should_use_dio(struct kiocb *iocb, struct iov_iter *iter)
 {
 	/* Current offset must be aligned */
@@ -684,14 +685,10 @@ ssize_t scoutfs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	struct super_block *sb = inode->i_sb;
 	struct scoutfs_lock *scoutfs_inode_lock = NULL;
 	SCOUTFS_DECLARE_PER_TASK_ENTRY(pt_ent);
-	SCOUTFS_DECLARE_PER_TASK_ENTRY(pt_extent_ent);
 	DECLARE_DATA_WAIT(dw);
-	bool locked;
 	int ret;
 
 retry:
-	locked = false;
-
 	/* protect checked extents from release */
 	inode_lock(inode);
 	atomic_inc(&inode->i_dio_count);
@@ -702,12 +699,6 @@ retry:
 	if (ret)
 		goto out;
 
-	ret = lock_for_iomap_read(inode, false, &pt_extent_ent);
-	if (ret)
-		return ret;
-
-	locked = true;
-
 	if (scoutfs_per_task_add_excl(&si->pt_data_lock, &pt_ent, scoutfs_inode_lock)) {
 		ret = scoutfs_data_wait_check(inode, iocb->ki_pos, iov_iter_count(to), SEF_OFFLINE,
 					      SCOUTFS_IOC_DWO_READ, &dw, scoutfs_inode_lock);
@@ -720,11 +711,6 @@ retry:
 	ret = generic_file_read_iter(iocb, to);
 
 out:
-	if (locked) {
-		unlock_for_iomap_read(inode, &pt_extent_ent);
-		locked = false;
-	}
-
 	inode_dio_end(inode);
 	scoutfs_per_task_del(&si->pt_data_lock, &pt_ent);
 	scoutfs_unlock(sb, scoutfs_inode_lock, SCOUTFS_LOCK_READ);

kmod/src/iomap.c

@@ -124,6 +124,12 @@ static int scoutfs_iomap_begin_report(struct inode *inode, loff_t offset, loff_t
 	return ret;
 }
 
+const struct iomap_ops scoutfs_iomap_report_ops = {
+	.iomap_begin    = scoutfs_iomap_begin_report,
+};
+
+#ifdef KC_USE_IOMAP_FOR_IO
+
 static int scoutfs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 			       unsigned int flags, struct iomap *iomap,
 			       struct iomap *srcmap)
@@ -261,11 +267,8 @@ static int scoutfs_iomap_end(struct inode *inode, loff_t offset, loff_t length,
 	return ret;
 }
 
-const struct iomap_ops scoutfs_iomap_report_ops = {
-	.iomap_begin    = scoutfs_iomap_begin_report,
-};
-
 const struct iomap_ops scoutfs_iomap_ops = {
 	.iomap_begin	= scoutfs_iomap_begin,
 	.iomap_end	= scoutfs_iomap_end,
 };
+#endif