[Xen-devel] [PATCH for-4.5] pygrub: fix read sizes on FreeBSD

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

FreeBSD only allows reading multiples of sector size from raw disk devices
(character devices). This fix should only alter the behaviour of pygrub on
FreeBSD, the other supported OSes will continue using the same size.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
I request a code freeze exception on the basis that this is a bugfix and it
doesn't change the behaviour on platforms different than FreeBSD.
---
 tools/pygrub/src/pygrub | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/tools/pygrub/src/pygrub b/tools/pygrub/src/pygrub
index e73a174..1ae34a2 100644
--- a/tools/pygrub/src/pygrub
+++ b/tools/pygrub/src/pygrub
@@ -13,7 +13,7 @@
 # Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 #
 
-import os, sys, string, struct, tempfile, re, traceback
+import os, sys, string, struct, tempfile, re, traceback, stat
 import copy
 import logging
 import platform
@@ -29,6 +29,16 @@ import grub.ExtLinuxConf
 
 PYGRUB_VER = 0.6
 FS_READ_MAX = 1024 * 1024
+SECTOR_SIZE = 512
+
+def read_size_roundup(fd, size):
+    if platform.system() != 'FreeBSD':
+        return size
+    st = os.fstat(fd)
+    if (not stat.S_ISCHR(st.st_mode)):
+        return size
+    # Round up to sector size if it's a raw character device
+    return (((size)+((SECTOR_SIZE)-1))&(~((SECTOR_SIZE)-1)))
 
 def enable_cursor(ison):
     if ison:
@@ -45,7 +55,7 @@ DISK_TYPE_RAW, DISK_TYPE_HYBRIDISO, DISK_TYPE_DOS = range(3)
 def identify_disk_image(file):
     """Detect DOS partition table or HybridISO format."""
     fd = os.open(file, os.O_RDONLY)
-    buf = os.read(fd, 0x8006)
+    buf = os.read(fd, read_size_roundup(fd, 0x8006))
     os.close(fd)
 
     if len(buf) >= 512 and \
@@ -56,7 +66,6 @@ def identify_disk_image(file):
         return DISK_TYPE_DOS
     return DISK_TYPE_RAW
 
-SECTOR_SIZE=512
 DK_LABEL_LOC=1
 DKL_MAGIC=0xdabe
 V_ROOT=0x2
@@ -91,7 +100,7 @@ def get_fs_offset_gpt(file):
     i = partcount
     offsets = []
     while i>0:
-        buf = os.read(fd, partsize)
+        buf = os.read(fd, read_size_roundup(fd, partsize))
         offsets.append(struct.unpack("<Q", buf[32:40])[0] * SECTOR_SIZE)
         i -= 1
     os.close(fd)
-- 
1.9.3 (Apple Git-50)


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