Re: [PATCH v2] btrfs-progs: btrfs: implement 'start-sync' and 'wait-sync' commands

[Sage Weil <sage@newdream.net>]

On Tue, 2 Nov 2010, Goffredo Baroncelli wrote:
> Like the command "btrfs subvol snapshot", I think that it is better to add a 
> modifier instead of a new command.
> 
>  btrfs filesystem sync [--async]
> 
> Sorry if I noticed this too late. But I don't see a valid reason to add 
> another command. From a UI point of view the meaning of the command is the 
> same, change only slight the behavior.
> 
> Even tough I have to admint that "sync --async" sound strange. May be flush is 
> better ?
> > +	{ do_wait_sync, 2,
> > +	  "filesystem wait-sync", "<path> <transid>\n"
> > +	        "Wait for the transaction <transid> on the filesystem at 
> <path> to commit."
> > +	},
> 
> If I understood correctly this command may be used to wait the execution of 
> several commands: snapshot, subvolume removal, sync...
> I can suggest a more general name like:
> 
> # btrfs filesystem wait-transaction <path> <transid>.
> 
> (which may be shortened as "btrfs filesystem wait ..."). 

How about start-transaction and wait-transaction?  Or start-commit and 
wait-commit?  ('transaction' is a heavily overloaded term.)  IMO both 
would be less weird than sync --async.

> Another suggestion: instead of checking if the <transid> is 0, leave the 
> <transid> optional. If <transid> is omitted, then the function waits all the 
> running transaction.

Definitely.

> Finally I suggest to put a little note about the command behvior when a 
> transaction is started after the command execution: is there a risk of DOS ?

Okay.  There's no DOS risk (at least no more so than with while true ; do 
sync ; done).  It'll return immediately if transid has committed.  If 
transid is 0, it'll find the most recent committing or committed transid 
and wait for that.  If nothing is currently committing, it'll return 
immediately.

sage



> 
> Anyway great work.
> 
> Goffredo
> 
> 
> >  	{ do_resize, 2,
> >  	  "filesystem resize", "[+/-]<newsize>[gkm]|max <filesystem>\n"
> >  		"Resize the file system. If 'max' is passed, the filesystem\n"
> > diff --git a/btrfs_cmds.c b/btrfs_cmds.c
> > index 8031c58..736437d 100644
> > --- a/btrfs_cmds.c
> > +++ b/btrfs_cmds.c
> > @@ -526,6 +526,55 @@ int do_fssync(int argc, char **argv)
> >  	return 0;
> >  }
> >  
> > +int do_start_sync(int argc, char **argv)
> > +{
> > +	int fd, res;
> > +	char	*path = argv[1];
> > +	__u64 transid;
> > +
> > +	fd = open_file_or_dir(path);
> > +	if (fd < 0) {
> > +		fprintf(stderr, "ERROR: can't access to '%s'\n", path);
> > +		return 12;
> > +	}
> > +
> > +	printf("StartSync '%s'\n", path);
> > +	res = ioctl(fd, BTRFS_IOC_START_SYNC, &transid);
> > +	close(fd);
> > +	if( res < 0 ){
> > +		fprintf(stderr, "ERROR: unable to fs-syncing '%s'\n", path);
> > +		return 16;
> > +	} else {
> > +		printf("transid %llu\n", (unsigned long long)transid);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +int do_wait_sync(int argc, char **argv)
> > +{
> > +	int fd, res;
> > +	char	*path = argv[1];
> > +	__u64 transid = atoll(argv[2]);
> > +
> > +	fd = open_file_or_dir(path);
> > +	if (fd < 0) {
> > +		fprintf(stderr, "ERROR: can't access to '%s'\n", path);
> > +		return 12;
> > +	}
> > +
> > +	printf("WaitSync '%s' transid %llu\n", path, (unsigned long 
> long)transid);
> > +	res = ioctl(fd, BTRFS_IOC_WAIT_SYNC, &transid);
> > +	close(fd);
> > +	if( res < 0 ){
> > +		fprintf(stderr, "ERROR: unable to wait-sync on '%s' transid 
> %llu: %s\n", path,
> > +			(unsigned long long)transid, strerror(errno));
> > +		return 16;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  int do_scan(int argc, char **argv)
> >  {
> >  	int	i, fd;
> > diff --git a/btrfs_cmds.h b/btrfs_cmds.h
> > index 7bde191..84c489f 100644
> > --- a/btrfs_cmds.h
> > +++ b/btrfs_cmds.h
> > @@ -19,6 +19,8 @@ int do_clone(int nargs, char **argv);
> >  int do_delete_subvolume(int nargs, char **argv);
> >  int do_create_subvol(int nargs, char **argv);
> >  int do_fssync(int nargs, char **argv);
> > +int do_start_sync(int nargs, char **argv);
> > +int do_wait_sync(int nargs, char **argv);
> >  int do_defrag(int argc, char **argv);
> >  int do_show_filesystem(int nargs, char **argv);
> >  int do_add_volume(int nargs, char **args);
> > diff --git a/man/btrfs.8.in b/man/btrfs.8.in
> > index 26ef982..e87b5fe 100644
> > --- a/man/btrfs.8.in
> > +++ b/man/btrfs.8.in
> > @@ -19,6 +19,10 @@ btrfs \- control a btrfs filesystem
> >  .PP
> >  \fBbtrfs\fP \fBfilesystem sync\fP\fI <path> \fP
> >  .PP
> > +\fBbtrfs\fP \fBfilesystem start-sync\fP\fI <path> \fP
> > +.PP
> > +\fBbtrfs\fP \fBfilesystem wait-sync\fP\fI <path> <transid>\fP
> > +.PP
> >  \fBbtrfs\fP \fBfilesystem resize\fP\fI [+/\-]<size>[gkm]|max 
> <filesystem>\fP
> >  .PP
> >  \fBbtrfs\fP \fBdevice scan\fP\fI [<device> [<device>..]]\fP
> > @@ -115,6 +119,16 @@ all the block devices.
> >  Force a sync for the filesystem identified by \fI<path>\fR.
> >  .TP
> >  
> > +\fBfilesystem start-sync\fR\fI <path> \fR
> > +Start a sync operation for the filesystem identified by \fI<path>\fR.  A 
> transaction id
> > +is printed that can be waited on using the \fBfilesystem wait-sync\fR 
> command.
> > +.TP
> > +
> > +\fBfilesystem wait-sync\fR\fI <path> <transid>\fR
> > +Wait for a the transaction \fI<transid>\fR to commit to disk.  If 
> \fI<transid>\fR is zero,
> > +wait for any currently committing transaction to commit.
> > +.TP
> > +
> >  .\"
> >  .\" Some wording are extracted by the resize2fs man page
> >  .\"
> > -- 
> > 1.7.0
> > 
> > --
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> 
> 
> -- 
> gpg key@ keyserver.linux.it: Goffredo Baroncelli (ghigo) <kreijack@inwind.it>
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