[U-Boot] [PATCH 1/3] fat: write: fix broken write to fragmented files

[Oleksandr Suvorov]

On Mon, Sep 16, 2019 at 3:25 PM Marek Szyprowski
<m.szyprowski at samsung.com> wrote:
>
> 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 at samsung.com>

Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov at toradex.com>

> ---
>  fs/fat/fat_write.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
> index 729cf39630d..6cfa5b45652 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 - 1) != endclust)
> +                               break;
>                         if (IS_LAST_CLUST(newclust, mydata->fatsize))
>                                 break;
>                         if (CHECK_CLUST(newclust, mydata->fatsize)) {
> @@ -811,7 +813,7 @@ set_contents(fsdata *mydata, dir_entry *dentptr, loff_t pos, __u8 *buffer,
>                         offset = 0;
>                 else
>                         offset = pos - cur_pos;
> -               wsize = min(cur_pos + actsize, filesize) - pos;
> +               wsize = min_t(unsigned long long, actsize, filesize - cur_pos);
>                 if (get_set_cluster(mydata, curclust, offset,
>                                     buffer, wsize, &actsize)) {
>                         printf("Error get-and-setting cluster\n");
> @@ -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;
> --
> 2.17.1
>
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-- 
Best regards

Oleksandr Suvorov
cryosay at gmail.com