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rofiles-fuse: Rework to be based on nlink 

Programs like `useradd` try to `open(/etc/passwd, O_RDWR)` to append,
which didn't work with rofiles-fuse.  Thinking about this, I realized
that there's a simpler algorithm for "can we write to this file" which
is "does it have a hardlink count <= 1"?

Switching to this both drops complexity (we no longer need to keep a
hash table of files we created), and also lets useradd work.

Closes: #462
Approved by: jlebon
This commit is contained in:
Colin Walters 2016-08-16 09:26:16 -04:00 committed by Atomic Bot
parent 3469161e41
commit 77af6844d8
1 changed files with 43 additions and 88 deletions
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131
src/rofiles-fuse/main.c
View File

@ -39,7 +39,6 @@
// Global to store our read-write path
static int basefd = -1;
static GHashTable *created_devino_hash = NULL;
static inline const char *
ENSURE_RELPATH (const char *path)
@ -50,51 +49,6 @@ ENSURE_RELPATH (const char *path)
return path;
}
typedef struct {
dev_t dev;
ino_t ino;
} DevIno;
static guint
devino_hash (gconstpointer a)
{
DevIno *a_i = (gpointer)a;
return (guint) (a_i->dev + a_i->ino);
}
static int
devino_equal (gconstpointer a,
gconstpointer b)
{
DevIno *a_i = (gpointer)a;
DevIno *b_i = (gpointer)b;
return a_i->dev == b_i->dev
&& a_i->ino == b_i->ino;
}
static gboolean
devino_set_contains (dev_t dev, ino_t ino)
{
DevIno devino = { dev, ino };
return g_hash_table_contains (created_devino_hash, &devino);
}
static gboolean
devino_set_insert (dev_t dev, ino_t ino)
{
DevIno *devino = g_new (DevIno, 1);
devino->dev = dev;
devino->ino = ino;
return g_hash_table_add (created_devino_hash, devino);
}
static gboolean
devino_set_remove (dev_t dev, ino_t ino)
{
DevIno devino = { dev, ino };
return g_hash_table_remove (created_devino_hash, &devino);
}
static int
callback_getattr (const char *path, struct stat *st_data)
{
@ -188,15 +142,7 @@ callback_mkdir (const char *path, mode_t mode)
static int
callback_unlink (const char *path)
{
struct stat stbuf;
path = ENSURE_RELPATH (path);
if (fstatat (basefd, path, &stbuf, AT_SYMLINK_NOFOLLOW) == 0)
{
if (!S_ISDIR (stbuf.st_mode))
devino_set_remove (stbuf.st_dev, stbuf.st_ino);
}
if (unlinkat (basefd, path, 0) == -1)
return -errno;
return 0;
@ -250,6 +196,12 @@ callback_link (const char *from, const char *to)
return 0;
}
static gboolean
stbuf_is_regfile_hardlinked (struct stat *stbuf)
{
return S_ISREG (stbuf->st_mode) && stbuf->st_nlink > 1;
}
static int
can_write (const char *path)
{
@ -261,11 +213,8 @@ can_write (const char *path)
else
return -errno;
}
if (!S_ISDIR (stbuf.st_mode))
{
if (!devino_set_contains (stbuf.st_dev, stbuf.st_ino))
return -EROFS;
}
if (stbuf_is_regfile_hardlinked (&stbuf))
return -EROFS;
return 0;
}
@ -334,41 +283,49 @@ callback_utime (const char *path, struct utimbuf *buf)
static int
do_open (const char *path, mode_t mode, struct fuse_file_info *finfo)
{
const int flags = finfo->flags & O_ACCMODE;
int fd;
struct stat stbuf;
/* Support read only opens */
G_STATIC_ASSERT (O_RDONLY == 0);
path = ENSURE_RELPATH (path);
if (flags == 0)
fd = openat (basefd, path, flags);
if ((finfo->flags & O_ACCMODE) == O_RDONLY)
{
/* Read */
fd = openat (basefd, path, finfo->flags);
if (fd == -1)
return -errno;
}
else
{
const int forced_excl_flags = flags | O_CREAT | O_EXCL;
/* Do an exclusive open, don't allow writable fds for existing
files */
fd = openat (basefd, path, forced_excl_flags, mode);
/* If they didn't specify O_EXCL, give them EROFS if the file
* exists.
*/
if (fd == -1 && (flags & O_EXCL) == 0)
{
if (errno == EEXIST)
errno = EROFS;
}
else if (fd != -1)
{
if (fstat (fd, &stbuf) == -1)
return -errno;
devino_set_insert (stbuf.st_dev, stbuf.st_ino);
}
}
/* Write */
if (fd == -1)
return -errno;
/* We need to specially handle O_TRUNC */
fd = openat (basefd, path, finfo->flags & ~O_TRUNC, mode);
if (fd == -1)
return -errno;
if (fstat (fd, &stbuf) == -1)
{
(void) close (fd);
return -errno;
}
if (stbuf_is_regfile_hardlinked (&stbuf))
{
(void) close (fd);
return -EROFS;
}
/* Handle O_TRUNC here only after verifying hardlink state */
if (finfo->flags & O_TRUNC)
{
if (ftruncate (fd, 0) == -1)
{
(void) close (fd);
return -errno;
}
}
}
finfo->fh = fd;
@ -594,8 +551,6 @@ main (int argc, char *argv[])
exit (EXIT_FAILURE);
}
created_devino_hash = g_hash_table_new_full (devino_hash, devino_equal, g_free, NULL);
fuse_main (args.argc, args.argv, &callback_oper, NULL);
return 0;