On Wednesday 10 June 2009 07:17:23 Marcus Johansson wrote:
> I'm using pread/pwrite in my multi-threaded application. Ran into
> mysterious problems. I discovered that uClibc thinks that the kernel does
> not implement pread/pwrite (__NR_pread is not defined). __NR_pread64 is
> defined though. This make uClibc use a fake pread/pwrite instead, using
> three lseeks (one to save the old position, one to reposition and finally,
> after the read/write operation, one to restore the original position). This
> sequence is apparently not thread safe which causes my problems. The place
> this is implemented is libc/sysdeps/linux/common/pread_write.c.
>
> I'm using uClibc-0.9.29. Do you have any suggestions? Is this a bug or have
> I misconfigured? I have configured uClibc with LFS.
seems to be broken for most people. please try this patch:
diff --git a/libc/sysdeps/linux/common/pread_write.c
b/libc/sysdeps/linux/common/pread_write.c
index 83d5fdf..c800ee4 100644
--- a/libc/sysdeps/linux/common/pread_write.c
+++ b/libc/sysdeps/linux/common/pread_write.c
@@ -27,9 +27,13 @@ extern __typeof(pwrite64) __libc_pwrite64;
#include <bits/kernel_types.h>
-#ifdef __NR_pread
+#if defined(__NR_pread) && !defined(__NR_pread64)
+# define __NR_pread64 __NR_pread
+#endif
+
+#ifdef __NR_pread64
-# define __NR___syscall_pread __NR_pread
+# define __NR___syscall_pread __NR_pread64
static __inline__ _syscall5(ssize_t, __syscall_pread, int, fd, void *, buf,
size_t, count, off_t, offset_hi, off_t, offset_lo)
@@ -51,9 +55,13 @@ weak_alias(__libc_pread64,pread64)
#endif /* __NR_pread */
-#ifdef __NR_pwrite
+#if defined(__NR_pwrite) && !defined(__NR_pwrite64)
+# define __NR_pwrite64 __NR_pwrite
+#endif
+
+#ifdef __NR_pwrite64
-# define __NR___syscall_pwrite __NR_pwrite
+# define __NR___syscall_pwrite __NR_pwrite64
static __inline__ _syscall5(ssize_t, __syscall_pwrite, int, fd, const void *,
buf,
size_t, count, off_t, offset_hi, off_t, offset_lo)
@@ -74,7 +82,7 @@ weak_alias(__libc_pwrite64,pwrite64)
# endif /* __UCLIBC_HAS_LFS__ */
#endif /* __NR_pwrite */
-#if ! defined __NR_pread || ! defined __NR_pwrite
+#if ! defined __NR_pread64 || ! defined __NR_pwrite64
/* libc_hidden_proto(read) */
/* libc_hidden_proto(write) */
/* libc_hidden_proto(lseek) */
@@ -154,7 +162,7 @@ static ssize_t __fake_pread_write64(int fd, void *buf,
return result;
}
# endif /* __UCLIBC_HAS_LFS__ */
-#endif /* ! defined __NR_pread || ! defined __NR_pwrite */
+#endif /* ! defined __NR_pread64 || ! defined __NR_pwrite64 */
#ifndef __NR_pread
ssize_t __libc_pread(int fd, void *buf, size_t count, off_t offset)
-mike
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