[linux] Use fstat() rather than statx()

The statx() system call has a clean header file and a consistent
layout, but was unfortunately added only in kernel 4.11.

Using stat() or fstat() directly is extremely messy since glibc does
not necessarily use the kernel native data structures.  However, as
the only current use case is to obtain the length of an open file, we
can merely provide a wrapper that does precisely this.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

3 files changed, 8 insertions, 11 deletions

diff --git a/src/include/ipxe/linux_api.h b/src/include/ipxe/linux_api.h
index ab2e8014d..5b0b242d1 100644
--- a/src/include/ipxe/linux_api.h
+++ b/src/include/ipxe/linux_api.h
@@ -46,7 +46,6 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <linux/ioctl.h>
 #include <linux/poll.h>
 #include <linux/fs.h>
-#include <linux/stat.h>
 #define MAP_FAILED ( ( void * ) -1 )
 #endif
 
@@ -66,8 +65,7 @@ extern ssize_t __asmcall linux_read ( int fd, void *buf, size_t count );
 extern ssize_t __asmcall linux_write ( int fd, const void *buf, size_t count );
 extern int __asmcall linux_fcntl ( int fd, int cmd, ... );
 extern int __asmcall linux_ioctl ( int fd, unsigned long request, ... );
-extern int __asmcall linux_statx ( int dirfd, const char *pathname, int flags,
-				   unsigned int mask, struct statx *statxbuf );
+extern int __asmcall linux_fstat_size ( int fd, size_t *size );
 extern int __asmcall linux_poll ( struct pollfd *fds, unsigned int nfds,
 				  int timeout );
 extern int __asmcall linux_nanosleep ( const struct timespec *req,
diff --git a/src/interface/linux/linux_api.c b/src/interface/linux/linux_api.c
index 6fa2b0e76..d1f969aa7 100644
--- a/src/interface/linux/linux_api.c
+++ b/src/interface/linux/linux_api.c
@@ -200,14 +200,15 @@ int __asmcall linux_ioctl ( int fd, unsigned long request, ... ) {
 }
 
 /**
- * Wrap statx()
+ * Wrap part of fstat()
  *
  */
-int __asmcall linux_statx ( int dirfd, const char *pathname, int flags,
-			    unsigned int mask, struct statx *statxbuf ) {
+int __asmcall linux_fstat_size ( int fd, size_t *size ) {
+	struct stat stat;
 	int ret;
 
-	ret = statx ( dirfd, pathname, flags, mask, statxbuf );
+	ret = fstat ( fd, &stat );
+	*size = stat.st_size;
 	if ( ret == -1 )
 		linux_errno = errno;
 	return ret;
@@ -531,7 +532,7 @@ PROVIDE_IPXE_SYM ( linux_read );
 PROVIDE_IPXE_SYM ( linux_write );
 PROVIDE_IPXE_SYM ( linux_fcntl );
 PROVIDE_IPXE_SYM ( linux_ioctl );
-PROVIDE_IPXE_SYM ( linux_statx );
+PROVIDE_IPXE_SYM ( linux_fstat_size );
 PROVIDE_IPXE_SYM ( linux_poll );
 PROVIDE_IPXE_SYM ( linux_nanosleep );
 PROVIDE_IPXE_SYM ( linux_usleep );
diff --git a/src/interface/linux/linux_sysfs.c b/src/interface/linux/linux_sysfs.c
index 0b9f1f5d9..463bc2ab9 100644
--- a/src/interface/linux/linux_sysfs.c
+++ b/src/interface/linux/linux_sysfs.c
@@ -40,7 +40,6 @@ FILE_LICENCE ( GPL2_OR_LATER );
  * @ret len		Length read, or negative error
  */
 int linux_sysfs_read ( const char *filename, userptr_t *data ) {
-	struct statx statx;
 	size_t offset;
 	size_t len;
 	ssize_t read;
@@ -57,13 +56,12 @@ int linux_sysfs_read ( const char *filename, userptr_t *data ) {
 	}
 
 	/* Get file length */
-	if ( linux_statx ( fd, "", AT_EMPTY_PATH, STATX_SIZE, &statx ) == -1 ) {
+	if ( linux_fstat_size ( fd, &len ) == -1 ) {
 		rc = -ELINUX ( linux_errno );
 		DBGC ( filename, "LINUX could not stat %s: %s\n",
 		       filename, linux_strerror ( linux_errno ) );
 		goto err_stat;
 	}
-	len = statx.stx_size;
 
 	/* Allocate buffer */
 	*data = umalloc ( len );