From 112b6e5fc690b2a73b6ad8c92dc4645db08503b6 Mon Sep 17 00:00:00 2001

From: Nathaniel McCallum <npmccallum@redhat.com>

Date: Fri, 2 Mar 2018 08:40:18 -0500

Subject: [PATCH 3/8] Add btrfs subvolume support for grub2

In order to find the subvolume prefix from a given path, we parse

/proc/mounts. In cases where /proc/mounts doesn't contain the

filesystem, the caller can use the --mounts option to specify his own

mounts file.

Btrfs subvolumes are already supported by grub2 and by grub2-mkconfig.

Fixes #22

---

 grubby.c | 148 +++++++++++++++++++++++++++++++++++++++++++++++++++++--

 1 file changed, 143 insertions(+), 5 deletions(-)

diff --git a/grubby.c b/grubby.c

index a062ef8e567..96d252a0a83 100644

--- a/grubby.c

+++ b/grubby.c

@@ -68,6 +68,8 @@ int isEfi = 0;

 char *saved_command_line = NULL;

+const char *mounts = "/proc/mounts";

+

 /* comments get lumped in with indention */

 struct lineElement {

     char * item;

@@ -1834,6 +1836,129 @@ static int endswith(const char *s, char c)

 	return s[slen] == c;

 }

+typedef struct {

+	const char *start;

+	size_t      chars;

+} field;

+

+static int iscomma(int c)

+{

+	return c == ',';

+}

+

+static int isequal(int c)

+{

+	return c == '=';

+}

+

+static field findField(const field *in, typeof(isspace) *isdelim, field *out)

+{

+	field nxt = {};

+	size_t off = 0;

+

+	while (off < in->chars && isdelim(in->start[off]))

+		off++;

+

+	if (off == in->chars)

+		return nxt;

+

+	out->start = &in->start[off];

+	out->chars = 0;

+

+	while (off + out->chars < in->chars && !isdelim(out->start[out->chars]))

+		out->chars++;

+

+	nxt.start = out->start + out->chars;

+	nxt.chars = in->chars - off - out->chars;

+	return nxt;

+}

+

+static int fieldEquals(const field *in, const char *str)

+{

+	return in->chars == strlen(str) &&

+		strncmp(in->start, str, in->chars) == 0;

+}

+

+/* Parse /proc/mounts to determine the subvolume prefix. */

+static size_t subvolPrefix(const char *str)

+{

+	FILE *file = NULL;

+	char *line = NULL;

+	size_t prfx = 0;

+	size_t size = 0;

+

+	file = fopen(mounts, "r");

+	if (!file)

+		return 0;

+

+	for (ssize_t s; (s = getline(&line, &size, file)) >= 0; ) {

+		field nxt = { line, s };

+		field dev = {};

+		field path = {};

+		field type = {};

+		field opts = {};

+		field opt = {};

+

+		nxt = findField(&nxt, isspace, &dev;;

+		if (!nxt.start)

+			continue;

+

+		nxt = findField(&nxt, isspace, &path);

+		if (!nxt.start)

+			continue;

+

+		nxt = findField(&nxt, isspace, &type);

+		if (!nxt.start)

+			continue;

+

+		nxt = findField(&nxt, isspace, &opts);

+		if (!nxt.start)

+			continue;

+

+		if (!fieldEquals(&type, "btrfs"))

+			continue;

+

+		/* We have found a btrfs mount point. */

+

+		nxt = opts;

+		while ((nxt = findField(&nxt, iscomma, &opt)).start) {

+			field key = {};

+			field val = {};

+

+			opt = findField(&opt, isequal, &key);

+			if (!opt.start)

+				continue;

+

+			opt = findField(&opt, isequal, &val;;

+			if (!opt.start)

+				continue;

+

+			if (!fieldEquals(&key, "subvol"))

+				continue;

+

+			/* We have found a btrfs subvolume mount point. */

+

+			if (strncmp(val.start, str, val.chars))

+				continue;

+

+			if (val.start[val.chars - 1] != '/' &&

+				str[val.chars] != '/')

+				continue;

+

+			/* The subvolume mount point matches our input. */

+

+			if (prfx < val.chars)

+				prfx = val.chars;

+		}

+	}

+

+	dbgPrintf("%s(): str: '%s', prfx: '%s'\n", __FUNCTION__, str, prfx);

+

+	fclose(file);

+	free(line);

+	return prfx;

+}

+

 int suitableImage(struct singleEntry * entry, const char * bootPrefix,

 		  int skipRemoved, int flags) {

     struct singleLine * line;

@@ -2794,12 +2919,22 @@ struct singleLine * addLineTmpl(struct singleEntry * entry,

 	/* but try to keep the rootspec from the template... sigh */

 	if (tmplLine->type & (LT_HYPER|LT_KERNEL|LT_MBMODULE|LT_INITRD|LT_KERNEL_EFI|LT_INITRD_EFI|LT_KERNEL_16|LT_INITRD_16)) {

-            size_t rs = getRootSpecifier(tmplLine->elements[1].item);

+            const char *prfx = tmplLine->elements[1].item;

+            size_t rs = getRootSpecifier(prfx);

+            if (isinitrd(tmplLine->type)) {

+                for (struct singleLine *l = entry->lines;

+                     rs == 0 && l; l = l->next) {

+                    if (iskernel(l->type)) {

+                        prfx = l->elements[1].item;

+                        rs = getRootSpecifier(prfx);

+                    }

+                }

+            }

             if (rs > 0) {

                 free(newLine->elements[1].item);

-                newLine->elements[1].item = sdupprintf("%.*s%s", (int) rs,

-                    tmplLine->elements[1].item, val);

-	    }

+                newLine->elements[1].item = sdupprintf("%.*s%s",

+						       (int) rs, prfx, val);

+            }

 	}

     }

@@ -3738,7 +3873,7 @@ static size_t getRootSpecifier(const char *str)

         rs++;

     }

-    return rs;

+	return rs + subvolPrefix(str + rs);

 }

 static char * getInitrdVal(struct grubConfig * config,

@@ -4253,6 +4388,9 @@ int main(int argc, const char ** argv) {

 	{ "mbargs", 0, POPT_ARG_STRING, &newMBKernelArgs, 0, 

 	    _("default arguments for the new multiboot kernel or "

               "new arguments for multiboot kernel being updated"), NULL },

+	{ "mounts", 0, POPT_ARG_STRING, &mounts, 0,

+            _("path to fake /proc/mounts file (for testing only)"),

+            _("mounts") },

 	{ "bad-image-okay", 0, 0, &badImageOkay, 0,

 	    _("don't sanity check images in boot entries (for testing only)"), 

 	    NULL },

-- 

2.17.1