[linux] Add a generic function for reading files from sysfs

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

src/interface/linux/linux_api.c

@@ -32,6 +32,7 @@
 #include <sys/mman.h>
 #include <sys/socket.h>
 #include <sys/time.h>
+#include <sys/stat.h>
 #include <netinet/in.h>
 #include <ipxe/linux_api.h>
 #include <ipxe/slirp.h>
@@ -198,6 +199,20 @@ int __asmcall linux_ioctl ( int fd, unsigned long request, ... ) {
 	return ret;
 }
 
+/**
+ * Wrap statx()
+ *
+ */
+int __asmcall linux_statx ( int dirfd, const char *pathname, int flags,
+			    unsigned int mask, struct statx *statxbuf ) {
+	int ret;
+
+	ret = statx ( dirfd, pathname, flags, mask, statxbuf );
+	if ( ret == -1 )
+		linux_errno = errno;
+	return ret;
+}
+
 /**
  * Wrap poll()
  *
@@ -516,6 +531,7 @@ 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_poll );
 PROVIDE_IPXE_SYM ( linux_nanosleep );
 PROVIDE_IPXE_SYM ( linux_usleep );

src/interface/linux/linux_sysfs.c

@@ -0,0 +1,107 @@
+/*
+ * Copyright (C) 2021 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <string.h>
+#include <errno.h>
+#include <ipxe/umalloc.h>
+#include <ipxe/linux_api.h>
+#include <ipxe/linux.h>
+#include <ipxe/linux_sysfs.h>
+
+/** @file
+ *
+ * Linux sysfs files
+ *
+ */
+
+/**
+ * Read file from sysfs
+ *
+ * @v filename		Filename
+ * @v data		Data to fill in
+ * @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;
+	int fd;
+	int rc;
+
+	/* Open file */
+	fd = linux_open ( filename, O_RDONLY );
+	if ( fd < 0 ) {
+		rc = -ELINUX ( linux_errno );
+		DBGC ( filename, "LINUX could not open %s: %s\n",
+		       filename, linux_strerror ( linux_errno ) );
+		goto err_open;
+	}
+
+	/* Get file length */
+	if ( linux_statx ( fd, "", AT_EMPTY_PATH, STATX_SIZE, &statx ) == -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 );
+	if ( ! *data ) {
+		rc = -ENOMEM;
+		DBGC ( filename, "LINUX could not allocate %zd bytes for %s\n",
+		       len, filename );
+		goto err_alloc;
+	}
+
+	/* Read file */
+	for ( offset = 0 ; offset < len ; offset += read ) {
+		read = linux_read ( fd, user_to_virt ( *data, offset ), len );
+		if ( read < 0 ) {
+			DBGC ( filename, "LINUX could not read %s: %s\n",
+			       filename, linux_strerror ( linux_errno ) );
+			goto err_read;
+		}
+		if ( read == 0 ) {
+			rc = -EIO;
+			DBGC ( filename, "LINUX read underlength %s\n",
+			       filename );
+			goto err_eof;
+		}
+	}
+
+	/* Close file */
+	linux_close ( fd );
+
+	DBGC ( filename, "LINUX read %s\n", filename );
+	return len;
+
+ err_eof:
+ err_read:
+	ufree ( *data );
+ err_alloc:
+ err_stat:
+	linux_close ( fd );
+ err_open:
+	return rc;
+}