libmount: add mount support for loopdevs

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 227 insertions, 0 deletions

diff --git a/libmount/src/context_loopdev.c b/libmount/src/context_loopdev.c
new file mode 100644
index 000000000..6ed0df13e
--- /dev/null
+++ b/libmount/src/context_loopdev.c
@@ -0,0 +1,227 @@
+/*
+ * Copyright (C) 2011 Karel Zak <kzak@redhat.com>
+ *
+ * This file may be redistributed under the terms of the
+ * GNU Lesser General Public License.
+ */
+
+/*
+ * DOCS: - "lo@" prefix for fstype is unsupported
+ *	 - encyption= mount option for loop device is unssuported
+ */
+
+#include <blkid.h>
+
+#include "mountP.h"
+#include "loopdev.h"
+#include "linux_version.h"
+
+
+int mnt_context_is_loopdev(struct libmnt_context *cxt)
+{
+	const char *type, *src;
+	int fl;
+
+	assert(cxt);
+	/* The mount flags have to be merged, otherwise we have to use
+	 * expensive mnt_context_get_user_mflags() instead of cxt->user_mountflags. */
+	assert((cxt->flags & MNT_FL_MOUNTFLAGS_MERGED));
+
+	if (!cxt->fs)
+		return 0;
+	src = mnt_fs_get_srcpath(cxt->fs);
+	if (!src)
+		return 0;		/* backing file not set */
+
+	if (cxt->user_mountflags & (MNT_MS_LOOP |
+				    MNT_MS_OFFSET |
+				    MNT_MS_SIZELIMIT))
+		return 1;
+
+	if (cxt->mountflags & (MS_BIND | MS_MOVE | MS_PROPAGATION))
+		return 0;
+
+	/* Automatically create a loop device from a regular file if a filesystem
+	 * is not specified or the filesystem is known for libblkid (these
+	 * filesystems work with block devices only).
+	 *
+	 * Note that there is not a restriction (on kernel side) that prevents regular
+	 * file as a mount(2) source argument. A filesystem that is able to mount
+	 * regular files could be implemented.
+	 */
+	type = mnt_fs_get_fstype(cxt->fs);
+	fl = __mnt_fs_get_flags(cxt->fs);
+
+	if (!(fl && (MNT_FS_PSEUDO | MNT_FS_NET | MNT_FS_SWAP)) &&
+	    (!type || strcmp(type, "auto") == 0 || blkid_known_fstype(type))) {
+		struct stat st;
+
+		if (stat(src, &st) || !S_ISREG(st.st_mode))
+			return 0;
+	}
+
+	return 1;
+}
+
+int mnt_context_setup_loopdev(struct libmnt_context *cxt)
+{
+	const char *backing_file;
+	char *loopdev = NULL;
+	size_t len;
+	struct loopdev_cxt lc;
+	int rc, lo_flags = 0;
+
+	assert(cxt);
+	assert(cxt->fs);
+	assert((cxt->flags & MNT_FL_MOUNTFLAGS_MERGED));
+
+	backing_file = mnt_fs_get_srcpath(cxt->fs);
+	if (!backing_file)
+		return -EINVAL;
+
+	DBG(CXT, mnt_debug_h(cxt, "trying to setup loopdev for %s", backing_file));
+
+	if (cxt->mountflags & MS_RDONLY) {
+		DBG(CXT, mnt_debug_h(cxt, "enabling READ-ONLY flag"));
+		lo_flags |= LO_FLAGS_READ_ONLY;
+	}
+	loopcxt_init(&lc, 0);
+
+	
+	if ((cxt->user_mountflags & MNT_MS_LOOP) &&
+	    mnt_fs_get_option(cxt->fs, "loop", &loopdev, &len) == 0 && loopdev) {
+
+		char *tmp = strndup(loopdev, len);
+		if (!tmp)
+			rc = -ENOMEM;
+		else {
+			rc = loopcxt_set_device(&lc, tmp);
+			free(tmp);
+		}
+	}
+
+	/* since 2.6.37 we don't have to store backing filename to mtab
+	 * because kernel provides the name in /sys.
+	 */
+	if (get_linux_version() >= KERNEL_VERSION(2, 6, 37) ||
+	    !cxt->mtab_writable) {
+		DBG(CXT, mnt_debug_h(cxt, "enabling AUTOCLEAR flag"));
+		lo_flags |= LO_FLAGS_AUTOCLEAR;
+	}
+
+	do {
+		/* found free device */
+		if (!loopdev) {
+			rc = loopcxt_find_unused(&lc);
+			if (rc)
+				goto done;
+			DBG(CXT, mnt_debug_h(cxt, "trying to use %s",
+						loopcxt_get_device(&lc)));
+		}
+
+		/* set device attributes */
+		rc = loopcxt_set_backing_file(&lc, backing_file);
+		if (rc)
+			goto done;
+
+		loopcxt_set_flags(&lc, lo_flags);
+
+		/* setup the device */
+		rc = loopcxt_setup_device(&lc);
+		if (!rc)
+			break;		/* success */
+
+		if (loopdev || rc != -EBUSY) {
+			DBG(CXT, mnt_debug_h(cxt, "failed to setup device"));
+			break;
+		}
+		DBG(CXT, mnt_debug_h(cxt, "loopdev stolen...trying again"));
+	} while (1);
+
+	if (!rc)
+		rc = mnt_fs_set_source(cxt->fs, loopcxt_get_device(&lc));
+
+	if (!rc) {
+		/* success */
+		cxt->flags |= MNT_FL_LOOPDEV_READY;
+
+		if ((cxt->user_mountflags & MNT_MS_LOOP) &&
+		    loopcxt_is_autoclear(&lc))
+			/*
+			 * autoclear flag accepted by kernel, don't store
+			 * the "loop=" option to mtab.
+			 */
+			cxt->user_mountflags &= ~MNT_MS_LOOP;
+
+		if (!(cxt->mountflags & MS_RDONLY) &&
+		    loopcxt_is_readonly(&lc))
+			/*
+			 * mount planned read-write, but loopdev is read-only,
+			 * let's fix mount options...
+			 */
+			cxt->mountflags |= MS_RDONLY;
+
+
+		/* we have to keep the device open until mount(1),
+		 * otherwise it will auto-cleared by kernel
+		 */
+		cxt->loopdev_fd = loopcxt_get_fd(&lc);
+		loopcxt_set_fd(&lc, -1, 0);
+	}
+done:
+	loopcxt_deinit(&lc);
+	return rc;
+}
+
+/*
+ * Deletes loop device
+ */
+int mnt_context_delete_loopdev(struct libmnt_context *cxt)
+{
+	const char *src;
+	int rc;
+
+	assert(cxt);
+	assert(cxt->fs);
+
+	src = mnt_fs_get_srcpath(cxt->fs);
+	if (!src)
+		return -EINVAL;
+
+	if (cxt->loopdev_fd > -1)
+		close(cxt->loopdev_fd);
+
+	rc = loopdev_delete(src);
+	cxt->flags &= ~MNT_FL_LOOPDEV_READY;
+	cxt->loopdev_fd = -1;
+
+	DBG(CXT, mnt_debug_h(cxt, "loopdev deleted [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * Clears loopdev stuff in context, should be called after
+ * failed or successful mount(2).
+ */
+int mnt_context_clear_loopdev(struct libmnt_context *cxt)
+{
+	assert(cxt);
+
+	if (mnt_context_get_status(cxt) == 0 &&
+	    (cxt->flags & MNT_FL_LOOPDEV_READY)) {
+		/*
+		 * mount(2) failed, delete loopdev
+		 */
+		mnt_context_delete_loopdev(cxt);
+
+	} else if (cxt->loopdev_fd > -1) {
+		/*
+		 * mount(2) success, close the device
+		 */
+		DBG(CXT, mnt_debug_h(cxt, "closing loopdev FD"));
+		close(cxt->loopdev_fd);
+	}
+	cxt->loopdev_fd = -1;
+	return 0;
+}
+