Commit eae96caffc for qemu.org

commit eae96caffc98b9ad8ad3a56bf5f59576f3eb110f
Author: Hanna Czenczek <hreitz@redhat.com>
Date:   Mon Mar 9 16:08:49 2026 +0100

    fuse: Reduce max read size

    We are going to introduce parallel processing via coroutines, a maximum
    read size of 64 MB may be problematic, allowing users of the export to
    force us to allocate quite large amounts of memory with just a few
    requests.

    At least tone it down to 1 MB, which is still probably far more than
    enough.  (Larger requests are split automatically by the FUSE kernel
    driver anyway.)

    (Yes, we inadvertently already had parallel request processing due to
    nested polling before.  Better to fix this late than never.)

    Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
    Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
    Message-ID: <20260309150856.26800-19-hreitz@redhat.com>
    Reviewed-by: Kevin Wolf <kwolf@redhat.com>
    Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/export/fuse.c b/block/export/fuse.c
index bd099d1291..f32e74f39d 100644
--- a/block/export/fuse.c
+++ b/block/export/fuse.c
@@ -45,7 +45,7 @@
 #endif

 /* Prevent overly long bounce buffer allocations */
-#define FUSE_MAX_READ_BYTES (MIN(BDRV_REQUEST_MAX_BYTES, 64 * 1024 * 1024))
+#define FUSE_MAX_READ_BYTES (MIN(BDRV_REQUEST_MAX_BYTES, 1 * 1024 * 1024))
 #define FUSE_MAX_WRITE_BYTES (64 * 1024)

 /*