On Thu, Feb 27, 2020 at 04:21:51PM +0800, liaoweixiong wrote: > On 2020/2/26 AM 8:52, Kees Cook wrote: > > On Fri, Feb 07, 2020 at 08:25:45PM +0800, WeiXiong Liao wrote: > >> +obj-$(CONFIG_PSTORE_BLK) += pstore_blk.o > >> +pstore_blk-y += blkzone.o > > > > Why this dance with files? I would just expect: > > > > obj-$(CONFIG_PSTORE_BLK) += blkzone.o > > > > This makes the built module named blkzone.ko rather than > pstore_blk.ko. You can just do a regular build rule: obj-$(CONFIG_PSTORE_BLK) += blkzone.o > >> +#define BLK_SIG (0x43474244) /* DBGC */ > > > > I was going to suggest extracting PERSISTENT_RAM_SIG, renaming it and > > using it in here and in ram_core.c, but then I realize they're not > > marking the same structure. How about choosing a new magic sig for the > > blkzone data header? > > > > That's OK to me. I don't know if there is a rule to get a new magic? > In addition, all members of this structure are the same as > struct persistent_ram_buffer after patch 2. Maybe it's a good idea to > extract it > if you want to merge ramoops and pstore/blk. Okay, let's leave it as-is for now. > >> + uint32_t sig; > >> + atomic_t datalen; > >> + uint8_t data[]; > >> +}; > >> + > >> +/** > >> + * struct blkz_dmesg_header: dmesg information > > > > This is the on-disk structure also? > > > Yes. The structure blkz_buffer is a generic header for all recorder > zone, and the > structure blkz_dmesg_header is a header for dmesg, saved in > blkz_buffer->data. > The dmesg recorder use it to save it's specific attributes. Okay, can you add comments to distinguish the on-disk structures from the in-memory, etc? > >> +#define DMESG_HEADER_MAGIC 0x4dfc3ae5 > > > > How was this magic chosen? > > It's a random number. Maybe should I chose a meaningful magic? That's fine; just add a comment to say so. > >> + * @dirty: > >> + * mark whether the data in @buffer are dirty (not flush to storage yet) > >> + */ > > > > Thank you for the kerndoc! :) Is it linked to from any .rst files? > > > > I don't get your words. There is a document on the 6th patch. I don't know > whether it is what you want? Patch 6 is excellent; I think you might want to add references back to these kern-doc structures using the ".. kernel-doc:: fs/pstore/blkzone.c" syntax: https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html#including-kernel-doc-comments > >> +static int blkz_zone_write(struct blkz_zone *zone, > >> + enum blkz_flush_mode flush_mode, const char *buf, > >> + size_t len, unsigned long off) > >> +{ > >> + struct blkz_info *info = blkz_cxt.bzinfo; > >> + ssize_t wcnt = 0; > >> + ssize_t (*writeop)(const char *buf, size_t bytes, loff_t pos); > >> + size_t wlen; > >> + > >> + if (off > zone->buffer_size) > >> + return -EINVAL; > >> + wlen = min_t(size_t, len, zone->buffer_size - off); > >> + if (buf && wlen) { > >> + memcpy(zone->buffer->data + off, buf, wlen); > >> + atomic_set(&zone->buffer->datalen, wlen + off); > >> + } > > > > If you're expecting concurrent writers (use of atomic_set(), I would > > expect the whole write to be locked instead. (i.e. what happens if > > multiple callers call blkz_zone_write()?) > > > > I don't agree with it. The datalen will be updated everywhere. It's useless > to lock here. But there could be multiple writers; locking should be needed. > One more things. During the analysis, I found another problem. > Removing old files will cause new logs to be lost. Take console recorder as > am example. After new rebooting, new logs are saved to buf while old > logs are > saved to old_buf. If we remove old file at that time, not only old_buf > is freed, but > also length of buf for new data is reset to zero. The ramoops may also > has this > problem. Hmm. I'll need to double-check this. It's possible the call to persistent_ram_zap() in ramoops_pstore_erase() is not needed. > >> +static int blkz_recover_dmesg_data(struct blkz_context *cxt) > > > > What does "recover" mean in this context? Is this "read from storage"? > > Yes. "recover" means reading data back from storage. Okay. Please add some comments here. I would think of it more as "read" or "load". When I think of "recover" I think of "finding something that was lost". But the name isn't important as long as there is a comment somewhere about what it's doing. -Kees -- Kees Cook
