[reactos] 01/01: [FREELDR] Use less memory when doing unaligned reads on Btrfs

[Mark Harmstone]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=77e2dc42a0c3a58747d0b…

commit 77e2dc42a0c3a58747d0b86cf612a78f21e77162
Author:     Mark Harmstone <mark(a)harmstone.com>
AuthorDate: Fri Oct 11 00:32:14 2019 +0100
Commit:     Victor Perevertkin <victor(a)perevertkin.ru>
CommitDate: Wed Oct 30 22:57:25 2019 +0300

    [FREELDR] Use less memory when doing unaligned reads on Btrfs
---
 boot/freeldr/freeldr/lib/fs/btrfs.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/boot/freeldr/freeldr/lib/fs/btrfs.c b/boot/freeldr/freeldr/lib/fs/btrfs.c
index 2f763f061f9..f808cd27b08 100644
--- a/boot/freeldr/freeldr/lib/fs/btrfs.c
+++ b/boot/freeldr/freeldr/lib/fs/btrfs.c
@@ -704,20 +704,34 @@ static u64 btrfs_read_extent_reg(struct btrfs_path *path, struct
btrfs_file_exte
     if (extent->compression == BTRFS_COMPRESS_NONE)
     {
         physical += extent->offset + offset;
-        if (physical & (512 - 1))
+
+        /* If somebody tried to do unaligned access */
+        if (physical & (SECTOR_SIZE - 1))
         {
-            /* If somebody tried to do unaligned access */
-            physical -= offset;
-            temp_out = FrLdrTempAlloc(size + offset, TAG_BTRFS_FILE);
+            u32 shift;
+
+            temp_out = FrLdrTempAlloc(SECTOR_SIZE, TAG_BTRFS_FILE);
 
-            if (!disk_read(physical, temp_out, size + offset))
+            if (!disk_read(ALIGN_DOWN_BY(physical, SECTOR_SIZE), temp_out, SECTOR_SIZE))
             {
                 FrLdrTempFree(temp_out, TAG_BTRFS_FILE);
                 return READ_ERROR;
             }
 
-            memcpy(out, temp_out + offset, size);
+            shift = (u32)(physical & (SECTOR_SIZE - 1));
+
+            if (size <= SECTOR_SIZE - shift)
+            {
+                memcpy(out, temp_out + shift, size);
+                FrLdrTempFree(temp_out, TAG_BTRFS_FILE);
+                return size;
+            }
+
+            memcpy(out, temp_out + shift, SECTOR_SIZE - shift);
             FrLdrTempFree(temp_out, TAG_BTRFS_FILE);
+
+            if (!disk_read(physical + SECTOR_SIZE - shift, out + SECTOR_SIZE - shift,
size - SECTOR_SIZE + shift))
+                return READ_ERROR;
         } else
         {
             if (!disk_read(physical, out, size))