calculate max number of bytes that can be read or written by using

buf_int_ptr and buf_user_ptr to avoid any possible race with comedi_buf_put*().

diff --git a/comedi/comedi_fops.c b/comedi/comedi_fops.c
index da95d59869355f14ddfeaa5ed9d04ebb5062d505..1bf594c52f41cc34e70ad4bdc585b0acf87bf004 100644 (file)
--- a/comedi/comedi_fops.c
+++ b/comedi/comedi_fops.c
@@ -1349,11 +1349,10 @@ static ssize_t comedi_write_v22(struct file *file,const char *buf,size_t nbytes,
 
                n=nbytes;
 
-               m=async->data_len+async->buf_int_count-async->buf_user_count;
-
-               if(async->buf_user_ptr+m > async->data_len){
-                       m=async->data_len - async->buf_user_ptr;
-               }
+               if( async->buf_user_ptr < async->buf_int_ptr)
+                       m = async->buf_int_ptr - async->buf_user_ptr;
+               else
+                       m = async->data_len - async->buf_user_count;
 
                if(m<n)n=m;
 
@@ -1444,14 +1443,14 @@ static ssize_t comedi_read_v22(struct file * file,char *buf,size_t nbytes,loff_t
 
                n=nbytes;
 
-               m=async->buf_int_count-async->buf_user_count;
+               if(async->buf_int_ptr >= async->buf_user_ptr)
+                       m = async->buf_int_ptr - async->buf_user_ptr;
+               else
+                       m = async->data_len - async->buf_user_ptr;
 
-               if(async->buf_user_ptr+m > async->data_len){
-                       m=async->data_len - async->buf_user_ptr;
 #if 0
 printk("m is %d\n",m);
 #endif
-               }
                if(m<n)n=m;
 
                if(n==0){