[PATCH v4 1/6] fat: write: fix broken write to fragmented files

Lukasz Majewski
2019-12-05T16:52:10Z

Hi Tom, Matthias,

> The code for handing file overwrite incorrectly assumed that the file
> on disk is always contiguous. This resulted in corrupting disk
> structure every time when write to existing fragmented file happened.
> Fix this by adding proper check for cluster discontinuity and adjust
> chunk size on each partial write.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>
> This patch partially fixes the issue revealed by the following test
> script:
>

Tom could you pic this patch and the following one (2/6):
https://patchwork.ozlabs.org/patch/1203101/

to -master as a fix?

This seems like a _real_ fix for FAT.

The dfu part of this series IMHO shall be grabbed by Matthias or me into
the -next branch of u-boot-dfu/rpi4 tree.

I do guess that Matthias shall fetch this series as he is assigned to
it in the patchwork?
I'm fine for this as I've already acked / reviewed DFU part of this
series.

> --->8-fat_test1.sh---
> #!/bin/bash
> make sandbox_defconfig
> make
> dd if=/dev/zero of=/tmp/10M.img bs=1024 count=10k
> mkfs.vfat -v /tmp/10M.img
> cat >/tmp/cmds <<EOF
> x
> host bind 0 /tmp/10M.img
> fatls host 0
> mw 0x1000000 0x0a434241 0x1000 # "ABC\n"
> mw 0x1100000 0x0a464544 0x8000 # "DEF\n"
> fatwrite host 0 0x1000000 file0001.raw 0x1000
> fatwrite host 0 0x1000000 file0002.raw 0x1000
> fatwrite host 0 0x1000000 file0003.raw 0x1000
> fatwrite host 0 0x1000000 file0004.raw 0x1000
> fatwrite host 0 0x1000000 file0005.raw 0x1000
> fatrm host 0 file0002.raw
> fatrm host 0 file0004.raw
> fatls host 0
> fatwrite host 0 0x1100000 file0007.raw 0x4000
> fatwrite host 0 0x1100000 file0007.raw 0x4000
> reset
> EOF
> ./u-boot </tmp/cmds
> #verify
> rm -r /tmp/result /tmp/model
> mkdir /tmp/result
> mkdir /tmp/model
> yes ABC | head -c 4096 >/tmp/model/file0001.raw
> yes ABC | head -c 4096 >/tmp/model/file0003.raw
> yes ABC | head -c 4096 >/tmp/model/file0005.raw
> yes DEF | head -c 16384 >/tmp/model/file0007.raw
> mcopy -n -i /tmp/10M.img ::file0001.raw /tmp/result
> mcopy -n -i /tmp/10M.img ::file0003.raw /tmp/result
> mcopy -n -i /tmp/10M.img ::file0005.raw /tmp/result
> mcopy -n -i /tmp/10M.img ::file0007.raw /tmp/result
> hd /tmp/10M.img
> if diff -urq /tmp/model /tmp/result
> then
> echo Test okay
> else
> echo Test fail
> fi
> --->8---
>
> Overwritting a discontiguous test file (file0007.raw) no longer causes
> corruption to file0003.raw, which's data lies between the chunks of
> the test file. The amount of data written to disk is still incorrect,
> what causes damage to the file (file0005.raw), which's data lies next
> to the test file. This will be fixed by the next patch.
>
> Feel free to prepare a proper sandbox/py_test based tests based on the
> provided test scripts.
> ---
> fs/fat/fat_write.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
> index 729cf39630..f946030f7d 100644
> --- a/fs/fat/fat_write.c
> +++ b/fs/fat/fat_write.c
> @@ -794,6 +794,8 @@ set_contents(fsdata *mydata, dir_entry *dentptr,
> loff_t pos, __u8 *buffer,
> newclust = get_fatent(mydata, endclust);
>
> + if (newclust != endclust + 1)
> + break;
> if (IS_LAST_CLUST(newclust, mydata->fatsize))
> break;
> if (CHECK_CLUST(newclust, mydata->fatsize)) {
> @@ -824,8 +826,6 @@ set_contents(fsdata *mydata, dir_entry *dentptr,
> loff_t pos, __u8 *buffer, if (filesize <= cur_pos)
> break;
>
> - /* CHECK: newclust = get_fatent(mydata, endclust); */
> -
> if (IS_LAST_CLUST(newclust, mydata->fatsize))
> /* no more clusters */
> break;

Best regards,

Lukasz Majewski

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