Commit 5b3ddb17 authored by Jason Wessel's avatar Jason Wessel Committed by Tom Rini
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fs/fat/fat.c: Do not perform zero block reads if there are no blocks left



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.

---------------------------------
Signed-off-by: default avatarJason Wessel <jason.wessel@windriver.com>
Signed-off-by: default avatarJason Wessel <jason.wessel@windriver.com>
Reviewed-by: Tom Rini's avatarTom Rini <trini@konsulko.com>
parent f1c0b7cd
......@@ -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;
......
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