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Jeff Mahoney wrote:
> On systems with very large numbers (> 1600 or so) of SCSI devices,
> cat /proc/scsi/scsi ends up failing with -ENOMEM. This is due to
> the show routine simply iterating over all of the devices with
> bus_for_each_dev(), and trying to dump all of them into the buffer
> at the same time. On my test system (using scsi_debug with 4064 devices),
> the output ends up being ~ 632k, far more than kmalloc will typically allow.
>
> This patch uses seq_file directly instead of single_file, and breaks up
> the operations into the 4 seq_file callbacks. The result is that
> each show() operation only dumps ~ 180 bytes into the buffer at a time
> so we don't run out of memory.
>
> Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx>
>
> ---
>
> drivers/scsi/scsi_proc.c | 69 ++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 63 insertions(+), 6 deletions(-)
I thought I'd address one of the most obvious concerns with this patch
before it comes up. I'm not particularly thrilled about open coding the
klist stuff. I'm talking with a few people on expanding the interface to
make this not suck so bad.
- -Jeff
> diff -rup a/drivers/scsi/scsi_proc.c b/drivers/scsi/scsi_proc.c
> --- a/drivers/scsi/scsi_proc.c 2007-04-12 13:41:06.000000000 -0400
> +++ b/drivers/scsi/scsi_proc.c 2007-04-12 13:47:38.000000000 -0400
> @@ -294,20 +294,77 @@ static ssize_t proc_scsi_write(struct fi
> return err;
> }
>
> -static int proc_scsi_show(struct seq_file *s, void *p)
> +static struct device *next_device(struct klist_iter *i)
> {
> - seq_printf(s, "Attached devices:\n");
> - bus_for_each_dev(&scsi_bus_type, NULL, s, proc_print_scsidevice);
> - return 0;
> + struct klist_node *n = klist_next(i);
> + return n ? container_of(n, struct device, knode_bus) : NULL;
> +}
> +
> +static void *scsi_seq_start(struct seq_file *sfile, loff_t *pos)
> +{
> + struct klist_iter *iter;
> + struct device *dev = NULL;
> + loff_t l = *pos;
> +
> + iter = kmalloc(sizeof (*iter), GFP_KERNEL);
> + if (!iter)
> + return ERR_PTR(-ENOMEM);
> +
> + klist_iter_init_node(&scsi_bus_type.klist_devices, iter, NULL);
> +
> + do {
> + dev = next_device(iter);
> + } while (l-- && dev);
> +
> + sfile->private = iter;
> + return dev;
> }
>
> +static void *scsi_seq_next(struct seq_file *sfile, void *v, loff_t *pos)
> +{
> + struct klist_iter *iter = (struct klist_iter *)sfile->private;
> + ++*pos;
> + return next_device(iter);
> +}
> +
> +static void scsi_seq_stop(struct seq_file *sfile, void *v)
> +{
> + struct klist_iter *iter = (struct klist_iter *)sfile->private;
> + sfile->private = NULL;
> + klist_iter_exit(iter);
> + kfree(iter);
> +}
> +
> +static int scsi_seq_show(struct seq_file *sfile, void *v)
> +{
> + struct klist_iter *iter = (struct klist_iter *)sfile->private;
> + struct device *dev = (struct device *)v;
> + struct klist_node *head;
> +
> + spin_lock(&iter->i_klist->k_lock);
> + head = container_of(iter->i_klist->k_list.next,
> + struct klist_node, n_node);
> + if (&dev->knode_bus == head)
> + seq_puts(sfile, "Attached devices:\n");
> + spin_unlock(&iter->i_klist->k_lock);
> +
> + return proc_print_scsidevice(dev, sfile);
> +}
> +
> +static struct seq_operations scsi_seq_ops = {
> + .start = scsi_seq_start,
> + .next = scsi_seq_next,
> + .stop = scsi_seq_stop,
> + .show = scsi_seq_show
> +};
> +
> static int proc_scsi_open(struct inode *inode, struct file *file)
> {
> /*
> * We don't really needs this for the write case but it doesn't
> * harm either.
> */
> - return single_open(file, proc_scsi_show, NULL);
> + return seq_open(file, &scsi_seq_ops);
> }
>
> static struct file_operations proc_scsi_operations = {
> @@ -315,7 +372,7 @@ static struct file_operations proc_scsi_
> .read = seq_read,
> .write = proc_scsi_write,
> .llseek = seq_lseek,
> - .release = single_release,
> + .release = seq_release,
> };
>
> int __init scsi_init_procfs(void)
>
>
- --
Jeff Mahoney
SUSE Labs
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