Replacing the system call pread() with lseek()/xread()/lseek() sequence.

Using cygwin with cygwin.dll before 1.5.22 the system call pread() is buggy.
This patch introduces NO_PREAD. If NO_PREAD is set git uses a sequence of
lseek()/xread()/lseek() to emulate pread.

Signed-off-by: Stefan-W. Hahn <stefan.hahn@s-hahn.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 18 insertions, 0 deletions

diff --git a/compat/pread.c b/compat/pread.c
new file mode 100644
index 000000000..978cac4ec
--- /dev/null
+++ b/compat/pread.c
@@ -0,0 +1,18 @@
+#include "../git-compat-util.h"
+
+ssize_t git_pread(int fd, void *buf, size_t count, off_t offset)
+{
+        off_t current_offset;
+        ssize_t rc;
+
+        current_offset = lseek(fd, 0, SEEK_CUR);
+
+        if (lseek(fd, offset, SEEK_SET) < 0)
+                return -1;
+
+        rc = read_in_full(fd, buf, count);
+
+        if (current_offset != lseek(fd, current_offset, SEEK_SET))
+                return -1;
+        return rc;
+}