cdinit: Parameterise squashfs path (and *almost* scan /proc/cmdline for it)

1 files changed, 53 insertions, 7 deletions

diff --git a/cdinit.c b/cdinit.c
index 1cc7ba8..aadae37 100644
--- a/cdinit.c
+++ b/cdinit.c
@@ -1,6 +1,6 @@
 /*
  * cdinit - start up udev, find the squashfs, and get the hell out of dodge
- * Copyright (c) 2016 Adélie Linux Team.  All rights reserved.
+ * Copyright (c) 2016-2018 Adélie Linux Team.  All rights reserved.
  * Licensed under the NCSA open source license.
  * See LICENSE file included with this source for more information.
  */
@@ -23,6 +23,36 @@
 
 
 /*!
+ * @brief Grab a parameter out of /proc/cmdline, if it is set.
+ * @param param		The parameter you wish to read.
+ * @param def		The default value if no value is set (or NULL).
+ * @returns The value of the parameter as set in /proc/cmdline, or
+ *          the value of `default` if no value is set.
+ * @note If a parameter is passed on the command line but has no value
+ *       (ex: 'debug'), its value will not be returned.
+ */
+const char *get_param(const char *param, const char *def)
+{
+	int cmd_fd;
+
+	if(access("/proc/cmdline", R_OK) != 0)
+	{
+		fprintf(stderr, "can't access kernel command line\n");
+		return def;
+	}
+
+	cmd_fd = open("/proc/cmdline", O_RDONLY);
+	if(cmd_fd == -1)
+	{
+		fprintf(stderr, "can't open kernel command line\n");
+		return def;
+	}
+
+	close(cmd_fd);
+	return def;
+}
+
+/*!
  * @brief Invoke a specified command.  Return if it is run successfully.
  * @param command	User-readable description of what command is to run.
  * @param path		The full on-disk path to the executable to run.
@@ -77,11 +107,11 @@ bool cdi_invoke(const char *command, const char *path, char * const argv[])
  * multiple drives that all have media present.  We can narrow it down,
  * however:
  * 
- * - We know that our device will have 'adelie.squashfs'.
+ * - We know that our device will have the specified squashfs.
  * - We know it will be mountable without external helpers, as ISO9660,
  *   FAT, and HFS+ are built in to the kernel.
  */
-bool cdi_find_media(void)
+bool cdi_find_media(const char *squash_name)
 {
 	struct udev *udev;
 	struct udev_enumerate *dev_list;
@@ -153,12 +183,20 @@ bool cdi_find_media(void)
 		}
 		free(fstype);
 
-		if(access("/media/adelie.squashfs", F_OK) != 0)
+		if(chdir("/media") != 0)
+		{
+			fprintf(stderr, "cdi_find_media: error accessing %s:"
+					" %s\n", dev_node, strerror(errno));
+			umount("/media");
+			continue;
+		}
+		if(faccessat(AT_FDCWD, squash_name, F_OK, 0) != 0)
 		{
 #ifdef DEBUG
 			fprintf(stderr, "cdi_find_media: %s: system not found:"
 					" %s\n", dev_node, strerror(errno));
 #endif
+			chdir("/");
 			umount("/media");
 			continue;
 		}
@@ -168,9 +206,10 @@ bool cdi_find_media(void)
 			dev_node);
 #endif
 
-		int squash_fd = open("/media/adelie.squashfs", O_RDONLY);
+		int squash_fd = openat(AT_FDCWD, squash_name, O_RDONLY);
 		if(squash_fd == -1)
 		{
+			chdir("/");
 			umount("/media");
 			continue;
 		}
@@ -179,6 +218,7 @@ bool cdi_find_media(void)
 		if(dev_fd == -1)
 		{
 			close(squash_fd);
+			chdir("/");
 			umount("/media");
 			continue;
 		}
@@ -196,11 +236,13 @@ bool cdi_find_media(void)
 #endif
 			ioctl(dev_fd, LOOP_CLR_FD, 0);
 			close(dev_fd);
+			chdir("/");
 			umount("/media");
 			continue;
 		}
 
 		close(dev_fd);
+		chdir("/");
 		udev_device_unref(device);
 		device = NULL;
 		break;
@@ -217,6 +259,7 @@ bool cdi_find_media(void)
 int main(void)
 {
 	pid_t our_pid;
+	const char *squash;
 	bool found = false;
 	unsigned char tries = 4;
 
@@ -289,15 +332,18 @@ int main(void)
 		}
 	}
 
+	/* Figure out what our squashfs is named. */
+	squash = get_param("squashroot", "adelie.squashfs");
+
 	/* Now we need to iterate over the available block devices, trying to
 	 * find our CD media.
 	 */
-	found = cdi_find_media();
+	found = cdi_find_media(squash);
 	while(!found && tries--)
 	{
+		found = cdi_find_media(squash);
 		fprintf(stderr, "Attempting to acquiesce...\n");
 		sleep(5);
-		found = cdi_find_media();
 	}
 
 	if(!found)