Messages in this thread Patch in this message | | | Date | Mon, 25 May 2015 13:03:04 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH] zram: check compressor name before setting it |
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On (05/22/15 22:14), Minchan Kim wrote: > > > >second, there is not much value in exposing zcomp internals, > > > >especially when the result is just another line in dmesg output. > > > > > > From the other hand, the only valid values that can be written are > > > in 'comp_algorithm'. > > > So when writing other one, returning -EINVAL seems to be reasonable. > > > The user would get immediately information that he can't do that, > > > now the information can be very deferred in time. > > > > it's not. > > the error message appears in syslog right before we return -EINVAL > > back to user. > > Although Marcin's description is rather misleading, I like the patch. > Every admin doesn't watch dmesg output. Even people could change loglevel > simply so KERN_INFO would be void in that case.
there is no -EUNSPPORTEDCOMPRESSIONALGORITHM errno that we can return back to userspace and expect it [userspace] to magically transform it into a meaningful error message; users must check syslog/dmesg. that's the way it is.
# echo LZ4 > /sys/block/zram0/comp_algorithm # -bash: echo: write error: Device or resource busy
- hm.... why? - well, that's why: dmesg [ 249.745335] zram: Can't change algorithm for initialized device
> Instant error propagation is more strighforward for user point of view > rather than delaying with depending on another event.
I'd rather just add two lines of code, w/o making zcomp internals visible.
it seems that we are trying to solve a problem that does not really exist. I think what we really need to do is to rewrite zram documentation and to propose zramctl usage as a recommended way of managing zram devices. zramctl does not do `typo' errors. if somebody wants to configure zram manually, then he simply must check syslog. it's simple.
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drivers/block/zram/zcomp.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index a1a8b8e..d96da53 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -54,11 +54,16 @@ static struct zcomp_backend *backends[] = { static struct zcomp_backend *find_backend(const char *compress) { int i = 0; + while (backends[i]) { if (sysfs_streq(compress, backends[i]->name)) break; i++; } + + if (!backends[i]) + pr_err("Error: unknown compression algorithm: %s\n", + compress); return backends[i]; }
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