linux-ext4 - Re: [RFC 1/4] fs: Add generic file system event notifications

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Date:	Wed, 15 Apr 2015 22:46:23 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Beata Michalska <b.michalska@...sung.com>,
	linux-kernel@...r.kernel.org
CC:	tytso@....edu, adilger.kernel@...ger.ca, hughd@...gle.com,
	lczerner@...hat.com, hch@...radead.org, linux-ext4@...r.kernel.org,
	linux-mm@...ck.org, kyungmin.park@...sung.com, kmpark@...radead.org
Subject: Re: [RFC 1/4] fs: Add generic file system event notifications

On 4/15/15 2:15 AM, Beata Michalska wrote:
> Introduce configurable generic interface for file
> system-wide event notifications to provide file
> systems with a common way of reporting any potential
> issues as they emerge.
> 
> The notifications are to be issued through generic
> netlink interface, by a dedicated, for file system
> events, multicast group. The file systems might as
> well use this group to send their own custom messages.

...

> + 4.3 Threshold notifications:
> +
> + #include <linux/fs_event.h>
> + void fs_event_alloc_space(struct super_block *sb, u64 ncount);
> + void fs_event_free_space(struct super_block *sb, u64 ncount);
> +
> + Each filesystme supporting the treshold notifiactions should call
> + fs_event_alloc_space/fs_event_free_space repsectively whenever the
> + ammount of availbale blocks changes.
> + - sb:     the filesystem's super block
> + - ncount: number of blocks being acquired/released

so:

> +void fs_event_alloc_space(struct super_block *sb, u64 ncount)
> +{
> +	struct fs_trace_entry *en;
> +	s64 count;
> +
> +	spin_lock(&fs_trace_lock);

Every allocation/free for every supported filesystem system-wide will be
serialized on this global spinlock?  That sounds like a non-starter...

-Eric

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