kmsg - kmsg_dump() use iterator to receive log buffer content

Provide an iterator to receive the log buffer content, and convert all
kmsg_dump() users to it.

The structured data in the kmsg buffer now contains binary data, which
should no longer be copied verbatim to the kmsg_dump() users.

The iterator should provide reliable access to the buffer data, and also
supports proper log line-aware chunking of data while iterating.

Signed-off-by: Kay Sievers <kay@vrfy.org>
Tested-by: Tony Luck <tony.luck@intel.com>
Reported-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Tested-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

6 files changed, 258 insertions, 137 deletions

diff --git a/arch/powerpc/platforms/pseries/nvram.c b/arch/powerpc/platforms/pseries/nvram.c
index 36f957f31842..8733a86ad52e 100644
--- a/arch/powerpc/platforms/pseries/nvram.c
+++ b/arch/powerpc/platforms/pseries/nvram.c
@@ -68,9 +68,7 @@ static const char *pseries_nvram_os_partitions[] = {
 };
 
 static void oops_to_nvram(struct kmsg_dumper *dumper,
-                enum kmsg_dump_reason reason,
-                const char *old_msgs, unsigned long old_len,
-                const char *new_msgs, unsigned long new_len);
+                          enum kmsg_dump_reason reason);
 
 static struct kmsg_dumper nvram_kmsg_dumper = {
         .dump = oops_to_nvram
@@ -504,28 +502,6 @@ int __init pSeries_nvram_init(void)
 }
 
 /*
- * Try to capture the last capture_len bytes of the printk buffer.  Return
- * the amount actually captured.
- */
-static size_t capture_last_msgs(const char *old_msgs, size_t old_len,
-                                const char *new_msgs, size_t new_len,
-                                char *captured, size_t capture_len)
-{
-        if (new_len >= capture_len) {
-                memcpy(captured, new_msgs + (new_len - capture_len),
-                                                                capture_len);
-                return capture_len;
-        } else {
-                /* Grab the end of old_msgs. */
-                size_t old_tail_len = min(old_len, capture_len - new_len);
-                memcpy(captured, old_msgs + (old_len - old_tail_len),
-                                                                old_tail_len);
-                memcpy(captured + old_tail_len, new_msgs, new_len);
-                return old_tail_len + new_len;
-        }
-}
-
-/*
  * Are we using the ibm,rtas-log for oops/panic reports?  And if so,
  * would logging this oops/panic overwrite an RTAS event that rtas_errd
  * hasn't had a chance to read and process?  Return 1 if so, else 0.
@@ -541,27 +517,6 @@ static int clobbering_unread_rtas_event(void)
                                                 NVRAM_RTAS_READ_TIMEOUT);
 }
 
-/* Squeeze out each line's <n> severity prefix. */
-static size_t elide_severities(char *buf, size_t len)
-{
-        char *in, *out, *buf_end = buf + len;
-        /* Assume a <n> at the very beginning marks the start of a line. */
-        int newline = 1;
-
-        in = out = buf;
-        while (in < buf_end) {
-                if (newline && in+3 <= buf_end &&
-                                *in == '<' && isdigit(in[1]) && in[2] == '>') {
-                        in += 3;
-                        newline = 0;
-                } else {
-                        newline = (*in == '\n');
-                        *out++ = *in++;
-                }
-        }
-        return out - buf;
-}
-
 /* Derived from logfs_compress() */
 static int nvram_compress(const void *in, void *out, size_t inlen,
                                                         size_t outlen)
@@ -619,9 +574,7 @@ static int zip_oops(size_t text_len)
  * partition.  If that's too much, go back and capture uncompressed text.
  */
 static void oops_to_nvram(struct kmsg_dumper *dumper,
-                enum kmsg_dump_reason reason,
-                const char *old_msgs, unsigned long old_len,
-                const char *new_msgs, unsigned long new_len)
+                          enum kmsg_dump_reason reason)
 {
         static unsigned int oops_count = 0;
         static bool panicking = false;
@@ -660,14 +613,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
                 return;
 
         if (big_oops_buf) {
-                text_len = capture_last_msgs(old_msgs, old_len,
-                        new_msgs, new_len, big_oops_buf, big_oops_buf_sz);
-                text_len = elide_severities(big_oops_buf, text_len);
+                kmsg_dump_get_buffer(dumper, false,
+                                     big_oops_buf, big_oops_buf_sz, &text_len);
                 rc = zip_oops(text_len);
         }
         if (rc != 0) {
-                text_len = capture_last_msgs(old_msgs, old_len,
-                                new_msgs, new_len, oops_data, oops_data_sz);
+                kmsg_dump_rewind(dumper);
+                kmsg_dump_get_buffer(dumper, true,
+                                     oops_data, oops_data_sz, &text_len);
                 err_type = ERR_TYPE_KERNEL_PANIC;
                 *oops_len = (u16) text_len;
         }
diff --git a/arch/x86/platform/mrst/early_printk_mrst.c b/arch/x86/platform/mrst/early_printk_mrst.c
index 3c6e328483c7..028454f0c3a5 100644
--- a/arch/x86/platform/mrst/early_printk_mrst.c
+++ b/arch/x86/platform/mrst/early_printk_mrst.c
@@ -110,19 +110,16 @@ static struct kmsg_dumper dw_dumper;
 static int dumper_registered;
 
 static void dw_kmsg_dump(struct kmsg_dumper *dumper,
-                        enum kmsg_dump_reason reason,
-                        const char *s1, unsigned long l1,
-                        const char *s2, unsigned long l2)
+                         enum kmsg_dump_reason reason)
 {
-        int i;
+        static char line[1024];
+        size_t len;
 
         /* When run to this, we'd better re-init the HW */
         mrst_early_console_init();
 
-        for (i = 0; i < l1; i++)
-                early_mrst_console.write(&early_mrst_console, s1 + i, 1);
-        for (i = 0; i < l2; i++)
-                early_mrst_console.write(&early_mrst_console, s2 + i, 1);
+        while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len))
+                early_mrst_console.write(&early_mrst_console, line, len);
 }
 
 /* Set the ratio rate to 115200, 8n1, IRQ disabled */
diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index ae36d7e1e913..551e316e4454 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -304,32 +304,17 @@ static void find_next_position(struct mtdoops_context *cxt)
 }
 
 static void mtdoops_do_dump(struct kmsg_dumper *dumper,
-                enum kmsg_dump_reason reason, const char *s1, unsigned long l1,
-                const char *s2, unsigned long l2)
+                            enum kmsg_dump_reason reason)
 {
         struct mtdoops_context *cxt = container_of(dumper,
                         struct mtdoops_context, dump);
-        unsigned long s1_start, s2_start;
-        unsigned long l1_cpy, l2_cpy;
-        char *dst;
-
-        if (reason != KMSG_DUMP_OOPS &&
-            reason != KMSG_DUMP_PANIC)
-                return;
 
         /* Only dump oopses if dump_oops is set */
         if (reason == KMSG_DUMP_OOPS && !dump_oops)
                 return;
 
-        dst = cxt->oops_buf + MTDOOPS_HEADER_SIZE; /* Skip the header */
-        l2_cpy = min(l2, record_size - MTDOOPS_HEADER_SIZE);
-        l1_cpy = min(l1, record_size - MTDOOPS_HEADER_SIZE - l2_cpy);
-
-        s2_start = l2 - l2_cpy;
-        s1_start = l1 - l1_cpy;
-
-        memcpy(dst, s1 + s1_start, l1_cpy);
-        memcpy(dst + l1_cpy, s2 + s2_start, l2_cpy);
+        kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
+                             record_size - MTDOOPS_HEADER_SIZE, NULL);
 
         /* Panics must be written immediately */
         if (reason != KMSG_DUMP_OOPS)
@@ -375,6 +360,7 @@ static void mtdoops_notify_add(struct mtd_info *mtd)
                 return;
         }
 
+        cxt->dump.max_reason = KMSG_DUMP_OOPS;
         cxt->dump.dump = mtdoops_do_dump;
         err = kmsg_dump_register(&cxt->dump);
         if (err) {
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 82c585f715e3..03ce7a9b81cc 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -94,20 +94,15 @@ static const char *get_reason_str(enum kmsg_dump_reason reason)
  * as we can from the end of the buffer.
  */
 static void pstore_dump(struct kmsg_dumper *dumper,
-            enum kmsg_dump_reason reason,
-            const char *s1, unsigned long l1,
-            const char *s2, unsigned long l2)
+                        enum kmsg_dump_reason reason)
 {
-        unsigned long   s1_start, s2_start;
-        unsigned long   l1_cpy, l2_cpy;
-        unsigned long   size, total = 0;
-        char            *dst;
+        unsigned long   total = 0;
         const char      *why;
         u64             id;
-        int             hsize, ret;
         unsigned int    part = 1;
         unsigned long   flags = 0;
         int             is_locked = 0;
+        int             ret;
 
         why = get_reason_str(reason);
 
@@ -119,30 +114,25 @@ static void pstore_dump(struct kmsg_dumper *dumper,
                 spin_lock_irqsave(&psinfo->buf_lock, flags);
         oopscount++;
         while (total < kmsg_bytes) {
+                char *dst;
+                unsigned long size;
+                int hsize;
+                size_t len;
+
                 dst = psinfo->buf;
                 hsize = sprintf(dst, "%s#%d Part%d\n", why, oopscount, part);
                 size = psinfo->bufsize - hsize;
                 dst += hsize;
 
-                l2_cpy = min(l2, size);
-                l1_cpy = min(l1, size - l2_cpy);
-
-                if (l1_cpy + l2_cpy == 0)
+                if (!kmsg_dump_get_buffer(dumper, true, dst, size, &len))
                         break;
 
-                s2_start = l2 - l2_cpy;
-                s1_start = l1 - l1_cpy;
-
-                memcpy(dst, s1 + s1_start, l1_cpy);
-                memcpy(dst + l1_cpy, s2 + s2_start, l2_cpy);
-
                 ret = psinfo->write(PSTORE_TYPE_DMESG, reason, &id, part,
-                                   hsize + l1_cpy + l2_cpy, psinfo);
+                                    hsize + len, psinfo);
                 if (ret == 0 && reason == KMSG_DUMP_OOPS && pstore_is_mounted())
                         pstore_new_entry = 1;
-                l1 -= l1_cpy;
-                l2 -= l2_cpy;
-                total += l1_cpy + l2_cpy;
+
+                total += hsize + len;
                 part++;
         }
         if (in_nmi()) {
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 35f7237ec972..af4eb5a39d9a 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -21,6 +21,7 @@
  * is passed to the kernel.
  */
 enum kmsg_dump_reason {
+        KMSG_DUMP_UNDEF,
         KMSG_DUMP_PANIC,
         KMSG_DUMP_OOPS,
         KMSG_DUMP_EMERG,
@@ -31,23 +32,37 @@ enum kmsg_dump_reason {
 
 /**
  * struct kmsg_dumper - kernel crash message dumper structure
- * @dump:       The callback which gets called on crashes. The buffer is passed
- *              as two sections, where s1 (length l1) contains the older
- *              messages and s2 (length l2) contains the newer.
  * @list:       Entry in the dumper list (private)
+ * @dump:       Call into dumping code which will retrieve the data with
+ *              through the record iterator
+ * @max_reason: filter for highest reason number that should be dumped
  * @registered: Flag that specifies if this is already registered
  */
 struct kmsg_dumper {
-        void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason,
-                        const char *s1, unsigned long l1,
-                        const char *s2, unsigned long l2);
         struct list_head list;
-        int registered;
+        void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
+        enum kmsg_dump_reason max_reason;
+        bool active;
+        bool registered;
+
+        /* private state of the kmsg iterator */
+        u32 cur_idx;
+        u32 next_idx;
+        u64 cur_seq;
+        u64 next_seq;
 };
 
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
+bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+                        char *line, size_t size, size_t *len);
+
+bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+                          char *buf, size_t size, size_t *len);
+
+void kmsg_dump_rewind(struct kmsg_dumper *dumper);
+
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
 int kmsg_dump_unregister(struct kmsg_dumper *dumper);
@@ -56,6 +71,22 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
+bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+                          const char *line, size_t size, size_t *len)
+{
+        return false;
+}
+
+bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+                            char *buf, size_t size, size_t *len)
+{
+        return false;
+}
+
+void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+{
+}
+
 static inline int kmsg_dump_register(struct kmsg_dumper *dumper)
 {
         return -EINVAL;
diff --git a/kernel/printk.c b/kernel/printk.c
index f205c25c37e2..ceb4a2f775a1 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -909,7 +909,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                 /*
                  * Find first record that fits, including all following records,
                  * into the user-provided buffer for this dump.
-                */
+                 */
                 seq = clear_seq;
                 idx = clear_idx;
                 while (seq < log_next_seq) {
@@ -919,6 +919,8 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                         idx = log_next(idx);
                         seq++;
                 }
+
+                /* move first record forward until length fits into the buffer */
                 seq = clear_seq;
                 idx = clear_idx;
                 while (len > size && seq < log_next_seq) {
@@ -929,7 +931,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                         seq++;
                 }
 
-                /* last message in this dump */
+                /* last message fitting into this dump */
                 next_seq = log_next_seq;
 
                 len = 0;
@@ -2300,48 +2302,210 @@ module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
  * kmsg_dump - dump kernel log to kernel message dumpers.
  * @reason: the reason (oops, panic etc) for dumping
  *
- * Iterate through each of the dump devices and call the oops/panic
- * callbacks with the log buffer.
+ * Call each of the registered dumper's dump() callback, which can
+ * retrieve the kmsg records with kmsg_dump_get_line() or
+ * kmsg_dump_get_buffer().
  */
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
-        u64 idx;
         struct kmsg_dumper *dumper;
-        const char *s1, *s2;
-        unsigned long l1, l2;
         unsigned long flags;
 
         if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
                 return;
 
-        /* Theoretically, the log could move on after we do this, but
-           there's not a lot we can do about that. The new messages
-           will overwrite the start of what we dump. */
+        rcu_read_lock();
+        list_for_each_entry_rcu(dumper, &dump_list, list) {
+                if (dumper->max_reason && reason > dumper->max_reason)
+                        continue;
+
+                /* initialize iterator with data about the stored records */
+                dumper->active = true;
+
+                raw_spin_lock_irqsave(&logbuf_lock, flags);
+                dumper->cur_seq = clear_seq;
+                dumper->cur_idx = clear_idx;
+                dumper->next_seq = log_next_seq;
+                dumper->next_idx = log_next_idx;
+                raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+
+                /* invoke dumper which will iterate over records */
+                dumper->dump(dumper, reason);
+
+                /* reset iterator */
+                dumper->active = false;
+        }
+        rcu_read_unlock();
+}
+
+/**
+ * kmsg_dump_get_line - retrieve one kmsg log line
+ * @dumper: registered kmsg dumper
+ * @syslog: include the "<4>" prefixes
+ * @line: buffer to copy the line to
+ * @size: maximum size of the buffer
+ * @len: length of line placed into buffer
+ *
+ * Start at the beginning of the kmsg buffer, with the oldest kmsg
+ * record, and copy one record into the provided buffer.
+ *
+ * Consecutive calls will return the next available record moving
+ * towards the end of the buffer with the youngest messages.
+ *
+ * A return value of FALSE indicates that there are no more records to
+ * read.
+ */
+bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+                        char *line, size_t size, size_t *len)
+{
+        unsigned long flags;
+        struct log *msg;
+        size_t l = 0;
+        bool ret = false;
+
+        if (!dumper->active)
+                goto out;
 
         raw_spin_lock_irqsave(&logbuf_lock, flags);
-        if (syslog_seq < log_first_seq)
-                idx = syslog_idx;
-        else
-                idx = log_first_idx;
+        if (dumper->cur_seq < log_first_seq) {
+                /* messages are gone, move to first available one */
+                dumper->cur_seq = log_first_seq;
+                dumper->cur_idx = log_first_idx;
+        }
 
-        if (idx > log_next_idx) {
-                s1 = log_buf;
-                l1 = log_next_idx;
+        /* last entry */
+        if (dumper->cur_seq >= log_next_seq) {
+                raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+                goto out;
+        }
 
-                s2 = log_buf + idx;
-                l2 = log_buf_len - idx;
-        } else {
-                s1 = "";
-                l1 = 0;
+        msg = log_from_idx(dumper->cur_idx);
+        l = msg_print_text(msg, syslog,
+                              line, size);
+
+        dumper->cur_idx = log_next(dumper->cur_idx);
+        dumper->cur_seq++;
+        ret = true;
+        raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+out:
+        if (len)
+                *len = l;
+        return ret;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
+
+/**
+ * kmsg_dump_get_buffer - copy kmsg log lines
+ * @dumper: registered kmsg dumper
+ * @syslog: include the "<4>" prefixes
+ * @line: buffer to copy the line to
+ * @size: maximum size of the buffer
+ * @len: length of line placed into buffer
+ *
+ * Start at the end of the kmsg buffer and fill the provided buffer
+ * with as many of the the *youngest* kmsg records that fit into it.
+ * If the buffer is large enough, all available kmsg records will be
+ * copied with a single call.
+ *
+ * Consecutive calls will fill the buffer with the next block of
+ * available older records, not including the earlier retrieved ones.
+ *
+ * A return value of FALSE indicates that there are no more records to
+ * read.
+ */
+bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+                          char *buf, size_t size, size_t *len)
+{
+        unsigned long flags;
+        u64 seq;
+        u32 idx;
+        u64 next_seq;
+        u32 next_idx;
+        size_t l = 0;
+        bool ret = false;
+
+        if (!dumper->active)
+                goto out;
+
+        raw_spin_lock_irqsave(&logbuf_lock, flags);
+        if (dumper->cur_seq < log_first_seq) {
+                /* messages are gone, move to first available one */
+                dumper->cur_seq = log_first_seq;
+                dumper->cur_idx = log_first_idx;
+        }
+
+        /* last entry */
+        if (dumper->cur_seq >= dumper->next_seq) {
+                raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+                goto out;
+        }
+
+        /* calculate length of entire buffer */
+        seq = dumper->cur_seq;
+        idx = dumper->cur_idx;
+        while (seq < dumper->next_seq) {
+                struct log *msg = log_from_idx(idx);
+
+                l += msg_print_text(msg, true, NULL, 0);
+                idx = log_next(idx);
+                seq++;
+        }
+
+        /* move first record forward until length fits into the buffer */
+        seq = dumper->cur_seq;
+        idx = dumper->cur_idx;
+        while (l > size && seq < dumper->next_seq) {
+                struct log *msg = log_from_idx(idx);
 
-                s2 = log_buf + idx;
-                l2 = log_next_idx - idx;
+                l -= msg_print_text(msg, true, NULL, 0);
+                idx = log_next(idx);
+                seq++;
         }
+
+        /* last message in next interation */
+        next_seq = seq;
+        next_idx = idx;
+
+        l = 0;
+        while (seq < dumper->next_seq) {
+                struct log *msg = log_from_idx(idx);
+
+                l += msg_print_text(msg, syslog,
+                                    buf + l, size - l);
+
+                idx = log_next(idx);
+                seq++;
+        }
+
+        dumper->next_seq = next_seq;
+        dumper->next_idx = next_idx;
+        ret = true;
         raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+out:
+        if (len)
+                *len = l;
+        return ret;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
-        rcu_read_lock();
-        list_for_each_entry_rcu(dumper, &dump_list, list)
-                dumper->dump(dumper, reason, s1, l1, s2, l2);
-        rcu_read_unlock();
+/**
+ * kmsg_dump_rewind - reset the interator
+ * @dumper: registered kmsg dumper
+ *
+ * Reset the dumper's iterator so that kmsg_dump_get_line() and
+ * kmsg_dump_get_buffer() can be called again and used multiple
+ * times within the same dumper.dump() callback.
+ */
+void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+{
+        unsigned long flags;
+
+        raw_spin_lock_irqsave(&logbuf_lock, flags);
+        dumper->cur_seq = clear_seq;
+        dumper->cur_idx = clear_idx;
+        dumper->next_seq = log_next_seq;
+        dumper->next_idx = log_next_idx;
+        raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 }
+EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
 #endif