Re: [PATCH 2/6] bcachefs: Add ability to redirect log output

Brian Foster
2023-12-08T20:23:23Z

On Wed, Dec 06, 2023 at 03:33:06PM -0500, Kent Overstreet wrote:
> Upcoming patches are going to add two new ioctls for running fsck in the
> kernel, but pretending that we're running our normal userspace fsck.
>
> This patch adds some plumbing for redirecting our normal log messages
> away from the dmesg log to a thread_with_file file descriptor - via a
> struct log_output, which will be consumed by the fsck f_op's read method.
>
> The new ioctls will allow for running fsck in the kernel against an
> offline filesystem (without mounting it), and an online filesystem. For
> an offline filesystem we need a way to pass in a pointer to the
> log_output, which is done via a new hidden opts.h option.
>
> For online fsck, we can set c->output directly, but only want to
> redirect log messages from the thread running fsck - hence the new
> c->output_filter method.
>
> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
> ---
> fs/bcachefs/bcachefs.h | 54 +++++++++++++++++++++++++++++++-----------
> fs/bcachefs/opts.h | 5 ++++
> fs/bcachefs/super.c | 28 ++++++++++++++++++++++
> 3 files changed, 73 insertions(+), 14 deletions(-)
>
...
> diff --git a/fs/bcachefs/opts.h b/fs/bcachefs/opts.h
> index 8526f177450a..91026dfb8c83 100644
> --- a/fs/bcachefs/opts.h
> +++ b/fs/bcachefs/opts.h
> @@ -419,6 +419,11 @@ enum fsck_err_opts {
> OPT_BOOL(), \
> BCH2_NO_SB_OPT, false, \
> NULL, "Allocate the buckets_nouse bitmap") \
> + x(log_output, u64, \
> + 0, \
> + OPT_UINT(0, S64_MAX), \
> + BCH2_NO_SB_OPT, false, \
> + NULL, "Allocate the buckets_nouse bitmap") \

I assume you want to update the string to something more related. :)

Brian

> x(project, u8, \
> OPT_INODE, \
> OPT_BOOL(), \
> diff --git a/fs/bcachefs/super.c b/fs/bcachefs/super.c
> index e7f186b45df1..6c320defd593 100644
> --- a/fs/bcachefs/super.c
> +++ b/fs/bcachefs/super.c
> @@ -80,6 +80,32 @@ const char * const bch2_fs_flag_strs[] = {
> NULL
> };
>
> +void __bch2_print(struct bch_fs *c, const char *fmt, ...)
> +{
> + struct log_output *output = c->output;
> + va_list args;
> +
> + if (c->output_filter && c->output_filter != current)
> + output = NULL;
> +
> + va_start(args, fmt);
> + if (likely(!output)) {
> + vprintk(fmt, args);
> + } else {
> + unsigned long flags;
> +
> + if (fmt[0] == KERN_SOH[0])
> + fmt += 2;
> +
> + spin_lock_irqsave(&output->lock, flags);
> + prt_vprintf(&output->buf, fmt, args);
> + spin_unlock_irqrestore(&output->lock, flags);
> +
> + wake_up(&output->wait);
> + }
> + va_end(args);
> +}
> +
> #define KTYPE(type) \
> static const struct attribute_group type ## _group = { \
> .attrs = type ## _files \
> @@ -703,6 +729,8 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
> goto out;
> }
>
> + c->output = (void *)(unsigned long) opts.log_output;
> +
> __module_get(THIS_MODULE);
>
> closure_init(&c->cl, NULL);
> --
> 2.42.0
>
>