Sorry. I wasn't very unambiguous, was I? And I'm not sure now whether
you're meaning "How does fuse support relate to freezing block devices?"
or "What's this about fuse support?". Let me therefore seek to answer
both questions:
Higher level, I know (filesystems rather than block devices), but I was
meaning the general concept of blocking new requests and completing
existing ones worked fine for the supposedly impossible fuse support.
Re fuse support, let me start by saying "I know this doesn't handle all
situations, but I think it's a good enough proof-of-concept implementation".
I added some simple hooks to the code for submitting new work to fuse
threads.
#define FUSE_MIGHT_FREEZE(superblock, desc) \
do { \
int printed = 0; \
while(superblock->s_frozen != SB_UNFROZEN) { \
if (!printed) { \
printk("%d frozen in " desc ".\n", current->pid); \
printed = 1; \
} \
try_to_freeze(); \
yield(); \
} \
} while (0)
On top of this, I made a (too simple at the moment) freeze_filesystems
function which iterates through &super_blocks in reverse order, freezing
fuse filesystems or ordinary ones. I say 'too simple' because it doesn't
currently allow for the possibility of someone mounting (say) ext3 on
fuse, but that would just be an extension of what's already done.
The end result is:
int freeze_processes(void)
{
int error;
printk(KERN_INFO "Stopping fuse filesystems.\n");
freeze_filesystems(FS_FREEZER_FUSE);
freezer_state = FREEZER_FILESYSTEMS_FROZEN;
printk(KERN_INFO "Freezing user space processes ... ");
error = try_to_freeze_tasks(FREEZER_USER_SPACE);
if (error)
goto Exit;
printk(KERN_INFO "done.\n");
sys_sync();
printk(KERN_INFO "Stopping normal filesystems.\n");
freeze_filesystems(FS_FREEZER_NORMAL);
freezer_state = FREEZER_USERSPACE_FROZEN;
printk(KERN_INFO "Freezing remaining freezable tasks ... ");
error = try_to_freeze_tasks(FREEZER_KERNEL_THREADS);
if (error)
goto Exit;
printk(KERN_INFO "done.");
freezer_state = FREEZER_FULLY_ON;
Exit:
BUG_ON(in_atomic());
printk("\n");
return error;
}
Sorry if that's more info than you wanted.
Nigel
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