[PATCH 1/2] fuse: reflect cached blocksize if blocksize was changed

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As pointed out by Miklos[1], in the fuse_update_get_attr() path, the
attributes returned to stat may be cached values instead of fresh ones
fetched from the server. In the case where the server returned a
modified blocksize value, we need to cache it and reflect it back to
stat if values are not re-fetched since we now no longer directly change
inode->i_blkbits.

Link: https://lore.kernel.org/linux-fsdevel/CAJfpeguCOxeVX88_zPd1hqziB_C+tmfuDhZP5qO2nKmnb-dTUA@xxxxxxxxxxxxxx/ [1]

Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
Fixes: 542ede096e48 ("fuse: keep inode->i_blkbits constant)
---
 fs/fuse/dir.c    | 1 +
 fs/fuse/fuse_i.h | 6 ++++++
 fs/fuse/inode.c  | 5 +++++
 3 files changed, 12 insertions(+)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 2d817d7cab26..ebee7e0b1cd3 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1377,6 +1377,7 @@ static int fuse_update_get_attr(struct mnt_idmap *idmap, struct inode *inode,
 		generic_fillattr(idmap, request_mask, inode, stat);
 		stat->mode = fi->orig_i_mode;
 		stat->ino = fi->orig_ino;
+		stat->blksize = 1 << fi->cached_i_blkbits;
 		if (test_bit(FUSE_I_BTIME, &fi->state)) {
 			stat->btime = fi->i_btime;
 			stat->result_mask |= STATX_BTIME;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index ec248d13c8bf..db44d05c8d02 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -210,6 +210,12 @@ struct fuse_inode {
 	/** Reference to backing file in passthrough mode */
 	struct fuse_backing *fb;
 #endif
+
+	/*
+	 * The underlying inode->i_blkbits value will not be modified,
+	 * so preserve the blocksize specified by the server.
+	 */
+	unsigned char cached_i_blkbits;
 };
 
 /** FUSE inode state bits */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 67c2318bfc42..3bfd83469d9f 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -289,6 +289,11 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
 		}
 	}
 
+	if (attr->blksize)
+		fi->cached_i_blkbits = ilog2(attr->blksize);
+	else
+		fi->cached_i_blkbits = inode->i_sb->s_blocksize_bits;
+
 	/*
 	 * Don't set the sticky bit in i_mode, unless we want the VFS
 	 * to check permissions.  This prevents failures due to the
-- 
2.47.3





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