fs: fat: check for buffer size before reading blocks

This patch optimizes the commit mentioned below by avoiding running
a set of commands which are useless in the case when
size < mydata->sect_size and sect_count would be 0.

Fixes: 5b3ddb17ba ("fs/fat/fat.c: Do not perform zero block reads if there are no blocks left")
Signed-off-by: Ricardo Salveti <ricardo@foundries.io>
Co-developed-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 7021138b9874be25100954f39bfbc25cffb30102..65f77c4f75d956a28bb7490862a00456bba2350c 100644 (file)
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -275,22 +275,19 @@ get_cluster(fsdata *mydata, __u32 clustnum, __u8 *buffer, unsigned long size)
                        buffer += mydata->sect_size;
                        size -= mydata->sect_size;
                }
-       } else {
-               __u32 idx;
-
-               idx = size / mydata->sect_size;
-               if (idx == 0)
-                       ret = 0;
-               else
-                       ret = disk_read(startsect, idx, buffer);
-               if (ret != idx) {
+       } else if (size >= mydata->sect_size) {
+               __u32 bytes_read;
+               __u32 sect_count = size / mydata->sect_size;
+
+               ret = disk_read(startsect, sect_count, buffer);
+               if (ret != sect_count) {
                        debug("Error reading data (got %d)\n", ret);
                        return -1;
                }
-               startsect += idx;
-               idx *= mydata->sect_size;
-               buffer += idx;
-               size -= idx;
+               bytes_read = sect_count * mydata->sect_size;
+               startsect += sect_count;
+               buffer += bytes_read;
+               size -= bytes_read;
        }
        if (size) {
                ALLOC_CACHE_ALIGN_BUFFER(__u8, tmpbuf, mydata->sect_size);