While using u-boot with qemu's virtio driver I stumbled across a problem reading files less than sector size. On the real hardware the block reader seems ok with reading zero blocks, and while we could fix the virtio host side of qemu to deal with a zero block read instead of crashing, the u-boot fat driver should not be doing zero block reads in the first place. If you ask hardware to read zero blocks you are just going to get zero data. There may also be other hardware that responds similarly to the virtio interface so this is worth fixing.

Without the patch I get the following and have to restart qemu because it dies. --------------------------------- => fatls virtio 0:1 30 cmdline.txt => fatload virtio 0:1 ${loadaddr} cmdline.txt qemu-system-aarch64: virtio: zero sized buffers are not allowed ---------------------------------

With the patch I get the expected results. --------------------------------- => fatls virtio 0:1 30 cmdline.txt => fatload virtio 0:1 ${loadaddr} cmdline.txt 30 bytes read in 11 ms (2 KiB/s) => md.b ${loadaddr} 0x1E 40080000: 64 77 63 5f 6f 74 67 2e 6c 70 6d 5f 65 6e 61 62 dwc_otg.lpm_enab 40080010: 6c 65 3d 30 20 72 6f 6f 74 77 61 69 74 0a le=0 rootwait.

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Signed-off-by: Jason Wessel jason.wessel@windriver.com

Signed-off-by: Jason Wessel jason.wessel@windriver.com --- fs/fat/fat.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/fat/fat.c b/fs/fat/fat.c index 7fd29470c1..dfad1e910b 100644 --- a/fs/fat/fat.c +++ b/fs/fat/fat.c @@ -278,7 +278,10 @@ get_cluster(fsdata *mydata, __u32 clustnum, __u8 *buffer, unsigned long size) } } else { idx = size / mydata->sect_size; - ret = disk_read(startsect, idx, buffer); + if (idx == 0) + ret = 0; + else + ret = disk_read(startsect, idx, buffer); if (ret != idx) { debug("Error reading data (got %d)\n", ret); return -1;