From ef20cd33d3287ebead0d30f2e177fc57a97dc2d5 Mon Sep 17 00:00:00 2001
From: Mark Johnston <markj@FreeBSD.org>
Date: Thu, 28 Sep 2023 16:16:17 -0400
Subject: [PATCH] makefs/zfs: Ensure that the last block of a file has the
 right size

When copying a file's contents into the pool, a loop copies blocks of
the maximum size (128KB), allocating space from the vdev for each block.
The space allocator rounds up to the nearest block size, but for files
larger than the maximum size, this can result in the last block having a
smaller logical size than the rest of the blocks belonging to that
dnode.  This violates some ZFS invariants when appending to that file.

Modify fs_populate_file() to use the same block size for the final
block.

Reported by:	cperciva
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
---
 usr.sbin/makefs/zfs/fs.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/usr.sbin/makefs/zfs/fs.c b/usr.sbin/makefs/zfs/fs.c
index 0d85ea8eb9d..b0a4c639f25 100644
--- a/usr.sbin/makefs/zfs/fs.c
+++ b/usr.sbin/makefs/zfs/fs.c
@@ -515,7 +515,7 @@ fs_populate_file(fsnode *cur, struct fs_populate_arg *arg)
 	uint64_t dnid;
 	ssize_t n;
 	size_t bufsz;
-	off_t size, target;
+	off_t nbytes, reqbytes, size;
 	int fd;
 
 	assert(cur->type == S_IFREG);
@@ -546,29 +546,30 @@ fs_populate_file(fsnode *cur, struct fs_populate_arg *arg)
 	bufsz = sizeof(zfs->filebuf);
 	size = cur->inode->st.st_size;
 	c = dnode_cursor_init(zfs, arg->fs->os, dnode, size, 0);
-	for (off_t foff = 0; foff < size; foff += target) {
+	for (off_t foff = 0; foff < size; foff += nbytes) {
 		off_t loc, sofar;
 
 		/*
 		 * Fill up our buffer, handling partial reads.
 		 */
 		sofar = 0;
-		target = MIN(size - foff, (off_t)bufsz);
+		nbytes = MIN(size - foff, (off_t)bufsz);
 		do {
-			n = read(fd, buf + sofar, target);
+			n = read(fd, buf + sofar, nbytes);
 			if (n < 0)
 				err(1, "reading from '%s'", cur->name);
 			if (n == 0)
 				errx(1, "unexpected EOF reading '%s'",
 				    cur->name);
 			sofar += n;
-		} while (sofar < target);
+		} while (sofar < nbytes);
 
-		if (target < (off_t)bufsz)
-			memset(buf + target, 0, bufsz - target);
+		if (nbytes < (off_t)bufsz)
+			memset(buf + nbytes, 0, bufsz - nbytes);
 
-		loc = objset_space_alloc(zfs, arg->fs->os, &target);
-		vdev_pwrite_dnode_indir(zfs, dnode, 0, 1, buf, target, loc,
+		reqbytes = foff == 0 ? nbytes : MAXBLOCKSIZE;
+		loc = objset_space_alloc(zfs, arg->fs->os, &reqbytes);
+		vdev_pwrite_dnode_indir(zfs, dnode, 0, 1, buf, reqbytes, loc,
 		    dnode_cursor_next(zfs, c, foff));
 	}
 	eclose(fd);