On Fri, 2016-07-15 at 01:37 +0200, Benoît Thébaudeau wrote:
Dear Tien Fong,
On Thu, Jul 14, 2016 at 12:48 PM, Tien Fong Chee tfchee@altera.com wrote:
Dear Benoît,
On Wed, 2016-07-13 at 12:56 +0200, Benoît Thébaudeau wrote:
Dear Tien Fong Chee,
On Jul 13, 2016 at 11:01 AM, Tien Fong Chee wrote:
Single 64KB get_contents_vfatname_block global variable would be used for all FAT implementation instead of allocating additional two global variables which are get_denfromdir_block and do_fat_read_at_block. This implementation can help in saving up 128KB memory space.
Signed-off-by: Tien Fong Chee tfchee@altera.com Cc: Dinh Nguyen dinguyen@opensource.altera.com Cc: Dinh Nguyen dinh.linux@gmail.com Cc: ChinLiang clsee@altera.com Cc: Vagrant Cascadian vagrant@debian.org Cc: Simon Glass sjg@chromium.org Cc: Stephen Warren swarren@nvidia.com Cc: Benoît Thébaudeau benoit@wsystem.com
fs/fat/fat.c | 6 ++---- 1 files changed, 2 insertions(+), 4 deletions(-)
diff --git a/fs/fat/fat.c b/fs/fat/fat.c index 826bd85..5d1afe6 100644 --- a/fs/fat/fat.c +++ b/fs/fat/fat.c @@ -579,8 +579,7 @@ static __u8 mkcksum(const char name[8], const char ext[3])
- Get the directory entry associated with 'filename' from the
directory
- starting at 'startsect'
*/ -__u8 get_dentfromdir_block[MAX_CLUSTSIZE]
- __aligned(ARCH_DMA_MINALIGN);
+__u8 *get_dentfromdir_block = get_contents_vfatname_block;
static dir_entry *get_dentfromdir(fsdata *mydata, int startsect, char *filename, dir_entry *retdent, @@ -811,8 +810,7 @@ exit: return ret; }
-__u8 do_fat_read_at_block[MAX_CLUSTSIZE]
- __aligned(ARCH_DMA_MINALIGN);
+__u8 *do_fat_read_at_block = get_contents_vfatname_block;
int do_fat_read_at(const char *filename, loff_t pos, void *buffer, loff_t maxsize, int dols, int dogetsize, loff_t *size)
This probably breaks at least fat_write.c, which uses: memcpy(get_dentfromdir_block, get_contents_vfatname_block,
With this patch, this line code "memcpy(get_dentfromdir_block, get_contents_vfatname_block," is not required anymore since both get_dentfromdir_block and get_contents_vfatname_block are sharing the same content and memory. So, this line code can be removed or leaving in there. However, there is only one place within fill_dir_slot_buffer function where it can corrupt the the global memory, and it is fixed by replacing with local buffer. This was sent out with another patch called "[PATCH 1/2] fs/fat/fatwrite: Local variable as buffer to store dir_slot entries". Overall, applying these two patches, a lot memory space can be saved and fitting into small OCRAM, but need to be very careful when modifying the code related to global memory.
I get the point, but I am a bit concerned because these changes make the code even more fragile and hard to maintain than it currently is.
Yeah, i agree with you, and there is trade-off in saving the memory space.
Perhaps it would be time to switch to FatFs as previously suggested. Here is its memory usage: http://elm-chan.org/fsw/ff/en/appnote.html#memory
Cool. If i am not mistaken, this implementation would impact a lot of areas, especially interface level. What's about the testing? I am still voting for this simple patch changes, until we have enough resources to do the switching.
I've not checked in detail all the possible code paths, but for instance, if I look at get_vfatname(), it's called twice in fat.c, once with cluster and retdent pointing to somewhere in get_dentfromdir_block, and once with them pointing to somewhere in do_fat_read_at_block (through other pointer variables), while get_vfatname() may write to get_contents_vfatname_block. get_vfatname() then uses the original data pointed to by slotptr >= retdent. To make things worse, there is a memcpy (not memmove) from realdent, which may point to somewhere in get_contents_vfatname_block, to retdent. It's almost impossible for the involved buffer areas not to overlap in that case since a whole cluster is read.
Yeah, i know your concern. For our codes design at this moment, it still safe for those involved buffer areas to get overlaped, because most of them are referring the data after overlaping. fill_dir_slot function is the only corruption area i have found so far.
I also agree with Stephen's recommendations.
Best regards, Benoît