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rofiles: Add --copyup option
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Sadly https://sourceware.org/bugzilla/show_bug.cgi?id=22089 is I think going to
actually force us to cave here. Even if we got the glibc patch in today, we need
to support the RHEL glibc. See also discussion about fish as part of the general
Fedora tracker.

This is basically needed to unblock rpm-ostree unified core 🌐:
coreos/rpm-ostree#729

Closes: ostreedev#1377
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@cgwalters
cgwalters committed Dec 14, 2017
1 parent 3b73d02 commit 689fe28
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Showing 3 changed files with 116 additions and 32 deletions.
5 changes: 3 additions & 2 deletions src/rofiles-fuse/Makefile-inc.am
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Original file line number Diff line number Diff line change
Expand Up @@ -19,5 +19,6 @@ bin_PROGRAMS += rofiles-fuse

rofiles_fuse_SOURCES = src/rofiles-fuse/main.c

rofiles_fuse_CFLAGS = $(AM_CFLAGS) -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 $(BUILDOPT_FUSE_CFLAGS) $(OT_INTERNAL_GIO_UNIX_CFLAGS) -I$(srcdir)/libglnx $(NULL)
rofiles_fuse_LDADD = libglnx.la $(BUILDOPT_FUSE_LIBS) $(OT_INTERNAL_GIO_UNIX_LIBS)
rofiles_fuse_CFLAGS = $(AM_CFLAGS) -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 $(BUILDOPT_FUSE_CFLAGS) \
$(OT_INTERNAL_GIO_UNIX_CFLAGS) -I $(srcdir)/src/libostree -I$(srcdir)/libglnx
rofiles_fuse_LDADD = libglnx.la $(BUILDOPT_FUSE_LIBS) $(OT_INTERNAL_GIO_UNIX_LIBS) libostree-1.la
122 changes: 93 additions & 29 deletions src/rofiles-fuse/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,9 +35,14 @@
#include <glib.h>

#include "libglnx.h"
#include "ostree.h"

// Global to store our read-write path
static int basefd = -1;
/* Whether or not to automatically "copyup" (in overlayfs terms).
* What we're really doing is breaking hardlinks.
*/
static gboolean opt_copyup;

static inline const char *
ENSURE_RELPATH (const char *path)
Expand Down Expand Up @@ -200,52 +205,97 @@ callback_link (const char *from, const char *to)
/* Check whether @stbuf refers to a hardlinked regfile or symlink, and if so
* return -EROFS. Otherwise return 0.
*/
static int
can_write_stbuf (struct stat *stbuf)
static gboolean
can_write_stbuf (const struct stat *stbuf)
{
/* If it's not a regular file or symlink, ostree won't hardlink it, so allow
* writes - it might be a FIFO or device that somehow
* ended up underneath our mount.
*/
if (!(S_ISREG (stbuf->st_mode) || S_ISLNK (stbuf->st_mode)))
return 0;
return TRUE;
/* If the object isn't hardlinked, it's OK to write */
if (stbuf->st_nlink <= 1)
return 0;
return TRUE;
/* Otherwise, it's a hardlinked file or symlink; it must be
* immutable.
*/
return -EROFS;
return FALSE;
}

/* Check whether @path refers to a hardlinked regfile or symlink, and if so
* return -EROFS. Otherwise return 0.
*/
static int
can_write (const char *path)
gioerror_to_errno (GIOErrorEnum e)
{
struct stat stbuf;
if (fstatat (basefd, path, &stbuf, AT_SYMLINK_NOFOLLOW) == -1)
/* It's obviously crappy to have to do this but
* we also don't want to try to have "raw errno" versions
* of everything down in ostree_break_hardlink() so...
* let's just reverse map a few ones I think are going to be common.
*/
switch (e)
{
if (errno == ENOENT)
return 0;
case G_IO_ERROR_NOT_FOUND:
return ENOENT;
case G_IO_ERROR_IS_DIRECTORY:
return EISDIR;
case G_IO_ERROR_PERMISSION_DENIED:
return EPERM;
case G_IO_ERROR_NO_SPACE:
return ENOSPC;
default:
return EIO;
}
}

static int
verify_write_or_copyup (const char *path, const struct stat *stbuf)
{
struct stat stbuf_local;

/* If a stbuf wasn't provided, gather it now */
if (!stbuf)
{
if (fstatat (basefd, path, &stbuf_local, AT_SYMLINK_NOFOLLOW) == -1)
{
if (errno == ENOENT)
return 0;
else
return -errno;
}
stbuf = &stbuf_local;
}

/* Verify writability, if that fails, perform copy-up if enabled */
if (!can_write_stbuf (stbuf))
{
if (opt_copyup)
{
g_autoptr(GError) tmp_error = NULL;
if (!ostree_break_hardlink (basefd, path, FALSE, NULL, &tmp_error))
return -gioerror_to_errno ((GIOErrorEnum)tmp_error->code);
}
else
return -errno;
return -EROFS;
}
return can_write_stbuf (&stbuf);

return 0;
}

#define VERIFY_WRITE(path) do { \
int r = can_write (path); \
if (r != 0) \
return r; \
/* Given a path (which is absolute), convert it
* to a relative path (even for the caller) and
* perform either write verification or copy-up.
*/
#define PATH_WRITE_ENTRYPOINT(path) do { \
path = ENSURE_RELPATH (path); \
int r = verify_write_or_copyup (path, NULL); \
if (r != 0) \
return r; \
} while (0)

static int
callback_chmod (const char *path, mode_t mode)
{
path = ENSURE_RELPATH (path);
VERIFY_WRITE(path);
PATH_WRITE_ENTRYPOINT (path);

/* Note we can't use AT_SYMLINK_NOFOLLOW yet;
* https://marc.info/?l=linux-kernel&m=148830147803162&w=2
* https://marc.info/?l=linux-fsdevel&m=149193779929561&w=2
Expand All @@ -258,8 +308,8 @@ callback_chmod (const char *path, mode_t mode)
static int
callback_chown (const char *path, uid_t uid, gid_t gid)
{
path = ENSURE_RELPATH (path);
VERIFY_WRITE(path);
PATH_WRITE_ENTRYPOINT (path);

if (fchownat (basefd, path, uid, gid, AT_SYMLINK_NOFOLLOW) != 0)
return -errno;
return 0;
Expand All @@ -268,12 +318,9 @@ callback_chown (const char *path, uid_t uid, gid_t gid)
static int
callback_truncate (const char *path, off_t size)
{
glnx_autofd int fd = -1;
PATH_WRITE_ENTRYPOINT (path);

path = ENSURE_RELPATH (path);
VERIFY_WRITE(path);

fd = openat (basefd, path, O_NOFOLLOW|O_WRONLY);
glnx_autofd int fd = openat (basefd, path, O_NOFOLLOW|O_WRONLY);
if (fd == -1)
return -errno;

Expand All @@ -286,6 +333,9 @@ callback_truncate (const char *path, off_t size)
static int
callback_utimens (const char *path, const struct timespec tv[2])
{
/* This one isn't write-verified, we support changing times
* even for hardlinked files.
*/
path = ENSURE_RELPATH (path);

if (utimensat (basefd, path, tv, AT_SYMLINK_NOFOLLOW) == -1)
Expand Down Expand Up @@ -324,13 +374,22 @@ do_open (const char *path, mode_t mode, struct fuse_file_info *finfo)
return -errno;
}

int r = can_write_stbuf (&stbuf);
int r = verify_write_or_copyup (path, &stbuf);
if (r != 0)
{
(void) close (fd);
return r;
}

/* In the copyup case, we need to re-open */
if (opt_copyup)
{
(void) close (fd);
fd = openat (basefd, path, finfo->flags & ~O_TRUNC, mode);
if (fd == -1)
return -errno;
}

/* Handle O_TRUNC here only after verifying hardlink state */
if (finfo->flags & O_TRUNC)
{
Expand Down Expand Up @@ -521,6 +580,7 @@ struct fuse_operations callback_oper = {
enum {
KEY_HELP,
KEY_VERSION,
KEY_COPYUP,
};

static void
Expand Down Expand Up @@ -565,6 +625,9 @@ rofs_parse_opt (void *data, const char *arg, int key,
case KEY_HELP:
usage (outargs->argv[0]);
exit (EXIT_SUCCESS);
case KEY_COPYUP:
opt_copyup = TRUE;
return 0;
default:
fprintf (stderr, "see `%s -h' for usage\n", outargs->argv[0]);
exit (EXIT_FAILURE);
Expand All @@ -577,6 +640,7 @@ static struct fuse_opt rofs_opts[] = {
FUSE_OPT_KEY ("--help", KEY_HELP),
FUSE_OPT_KEY ("-V", KEY_VERSION),
FUSE_OPT_KEY ("--version", KEY_VERSION),
FUSE_OPT_KEY ("--copyup", KEY_COPYUP),
FUSE_OPT_END
};

Expand Down
21 changes: 20 additions & 1 deletion tests/test-rofiles-fuse.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ skip_without_user_xattrs

setup_test_repository "bare"

echo "1..8"
echo "1..10"

cd ${test_tmpdir}
mkdir mnt
Expand Down Expand Up @@ -117,3 +117,22 @@ echo "ok checkout copy fallback"

# check that O_RDONLY|O_CREAT is handled correctly; used by flock(1) at least
flock mnt/nonexistent-file echo "ok create file in ro mode"
echo "ok flock"

# And now with --copyup enabled

fusermount -u ${test_tmpdir}/mnt
assert_not_has_file mnt/firstfile
rofiles-fuse --copyup checkout-test2 mnt
assert_file_has_content mnt/firstfile first
echo "ok copyup mount"

firstfile_orig_inode=$(stat -c %i checkout-test2/firstfile)
for path in firstfile{,-link}; do
echo truncating > mnt/${path}
assert_file_has_content mnt/${path} truncating
done
firstfile_new_inode=$(stat -c %i checkout-test2/firstfile)
assert_not_streq "${firstfile_orig_inode}" "${firstfile_new_inode}"

echo "ok copyup"

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