From 42d5ab3a72d852158098ad648af234dc3bb9a4db Mon Sep 17 00:00:00 2001
From: Morgan Stuart <morgansstuart243@gmail.com>
Date: Sun, 3 May 2015 21:33:40 -0400
Subject: [PATCH] Offset and length arguments added to fincore method

mmap call begins at offset bytes and maps length bytes. Offset defaults
to zero (start of file). A length of 0 will mmap the entire file minus
the offset value. Length also defaults to zero, therefore, the behavior
should stay the same for any legacy users.
---
 ftools.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)
 mode change 100644 => 100755 ftools.c

diff --git a/ftools.c b/ftools.c
old mode 100644
new mode 100755
index 5fec83b..2996eb0
--- a/ftools.c
+++ b/ftools.c
@@ -5,17 +5,22 @@
 #include <linux/fadvise.h>
 #include <sys/syscall.h>
 
-static PyObject *ftools_fincore(PyObject *self, PyObject *args) {
+static PyObject *ftools_fincore(PyObject *self, PyObject *args, PyObject *keywds) {
     PyObject *ret;
     int fd;
+    unsigned long offset = 0;
+    unsigned long length = 0;
     void *file_mmap;
     unsigned char *mincore_vec;
     struct stat file_stat;
     ssize_t page_size = getpagesize();
     ssize_t vec_size;
 
-    if(!PyArg_ParseTuple(args, "i", &fd)) {
-        return NULL;
+    static char *kwlist[] = {"fd", "offset", "length", NULL};
+
+    if (!PyArg_ParseTupleAndKeywords(args, keywds, "i|kk", kwlist, 
+                                     &fd, &offset, &length)) {
+        return NULL; 
     }
 
     if(fstat(fd, &file_stat) < 0) {
@@ -28,21 +33,24 @@ static PyObject *ftools_fincore(PyObject *self, PyObject *args) {
         return NULL;
     }
 
-    file_mmap = mmap((void *)0, file_stat.st_size, PROT_NONE, MAP_SHARED, fd, 0);
+    if ( length == 0 )
+        length = file_stat.st_size - offset;
+
+    file_mmap = mmap((void *)0, length, PROT_NONE, MAP_SHARED, fd, offset);
 
     if(file_mmap == MAP_FAILED) {
         PyErr_SetString(PyExc_IOError, "Could not mmap file");
         return NULL;
     }
 
-    vec_size = (file_stat.st_size + page_size - 1) / page_size;
+    vec_size = (length + page_size - 1) / page_size;
     mincore_vec = calloc(1, vec_size);
 
     if(mincore_vec == NULL) {
         return PyErr_NoMemory();
     }
 
-    if(mincore(file_mmap, file_stat.st_size, mincore_vec) != 0) {
+    if(mincore(file_mmap, length, mincore_vec) != 0) {
         PyErr_SetFromErrno(PyExc_OSError);
         PyErr_SetString(PyExc_OSError, "Could not call mincore for file");
         return NULL;
@@ -50,7 +58,7 @@ static PyObject *ftools_fincore(PyObject *self, PyObject *args) {
 
     ret = Py_BuildValue("s#", mincore_vec, vec_size);
     free(mincore_vec);
-    munmap(file_mmap, file_stat.st_size);
+    munmap(file_mmap, length);
     return ret;
 }
 
@@ -176,7 +184,7 @@ static PyObject *ftools_fadvise(PyObject *self, PyObject *args, PyObject *keywds
 }
 
 static PyMethodDef FtoolsMethods[] = {
-    {"fincore", ftools_fincore, METH_VARARGS, "Return the mincore structure for the given file."},
+    {"fincore", ftools_fincore, METH_KEYWORDS, "Return the mincore structure for the given file."},
     {"fincore_ratio", ftools_fincore_ratio, METH_VARARGS, "Return a int two tuple indicating file in page cache ratio."},
     {"fadvise", (PyCFunction) ftools_fadvise, METH_KEYWORDS, "fadvise system call for Python!"},
     {NULL, NULL, 0, NULL}