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From 283df68dbc1d90cad21beec6563215c26c69ec2c Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Fri, 24 Jul 2015 01:55:45 +0200
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Subject: [PATCH] journal: avoid mapping empty data and field hash tables
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When a new journal file is created we write the header first, then sync
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and only then create the data and field hash tables in them. That means
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to other processes it might appear that the files have a valid header
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but not data and field hash tables. Our reader code should be able to
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deal with this.
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With this change we'll not map the two hash tables right-away after
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opening a file for reading anymore (because that will of course fail if
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the objects are missing), but delay this until the first time we access
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them. On top of that, when we want to look something up in the hash
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tables and we notice they aren't initialized yet, we consider them
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empty.
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This improves handling of some journal files reported in #487.
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Cherry-picked from: dade37d403f1b8c1d7bb2efbe2361f2a3e999613
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Related: #1350232
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---
23b3cf
 src/journal/journal-file.c   | 37 +++++++++++++++++++++++++-----------
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 src/journal/journal-file.h   |  3 +++
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 src/journal/journal-verify.c | 14 ++++++++++++++
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 3 files changed, 43 insertions(+), 11 deletions(-)
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diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
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index 892fe47340..ef18497879 100644
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--- a/src/journal/journal-file.c
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+++ b/src/journal/journal-file.c
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@@ -656,13 +656,16 @@ static int journal_file_setup_field_hash_table(JournalFile *f) {
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         return 0;
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 }
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-static int journal_file_map_data_hash_table(JournalFile *f) {
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+int journal_file_map_data_hash_table(JournalFile *f) {
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         uint64_t s, p;
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         void *t;
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         int r;
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         assert(f);
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+        if (f->data_hash_table)
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+                return 0;
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+
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         p = le64toh(f->header->data_hash_table_offset);
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         s = le64toh(f->header->data_hash_table_size);
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@@ -678,13 +681,16 @@ static int journal_file_map_data_hash_table(JournalFile *f) {
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         return 0;
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 }
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-static int journal_file_map_field_hash_table(JournalFile *f) {
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+int journal_file_map_field_hash_table(JournalFile *f) {
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         uint64_t s, p;
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         void *t;
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         int r;
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         assert(f);
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+        if (f->field_hash_table)
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+                return 0;
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+
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         p = le64toh(f->header->field_hash_table_offset);
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         s = le64toh(f->header->field_hash_table_size);
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@@ -803,10 +809,18 @@ int journal_file_find_field_object_with_hash(
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         assert(f);
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         assert(field && size > 0);
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+        /* If the field hash table is empty, we can't find anything */
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+        if (le64toh(f->header->field_hash_table_size) <= 0)
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+                return 0;
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+
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+        /* Map the field hash table, if it isn't mapped yet. */
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+        r = journal_file_map_field_hash_table(f);
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+        if (r < 0)
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+                return r;
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+
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         osize = offsetof(Object, field.payload) + size;
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         m = le64toh(f->header->field_hash_table_size) / sizeof(HashItem);
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-
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         if (m <= 0)
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                 return -EBADMSG;
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@@ -866,6 +880,15 @@ int journal_file_find_data_object_with_hash(
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         assert(f);
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         assert(data || size == 0);
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+        /* If there's no data hash table, then there's no entry. */
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+        if (le64toh(f->header->data_hash_table_size) <= 0)
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+                return 0;
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+
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+        /* Map the data hash table, if it isn't mapped yet. */
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+        r = journal_file_map_data_hash_table(f);
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+        if (r < 0)
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+                return r;
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+
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         osize = offsetof(Object, data.payload) + size;
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         m = le64toh(f->header->data_hash_table_size) / sizeof(HashItem);
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@@ -2707,14 +2730,6 @@ int journal_file_open(
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 #endif
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         }
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-        r = journal_file_map_field_hash_table(f);
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-        if (r < 0)
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-                goto fail;
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-
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-        r = journal_file_map_data_hash_table(f);
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-        if (r < 0)
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-                goto fail;
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-
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         if (mmap_cache_got_sigbus(f->mmap, f->fd)) {
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                 r = -EIO;
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                 goto fail;
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diff --git a/src/journal/journal-file.h b/src/journal/journal-file.h
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index 0f29b092b7..c74ad5fc58 100644
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--- a/src/journal/journal-file.h
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+++ b/src/journal/journal-file.h
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@@ -234,3 +234,6 @@ static inline bool JOURNAL_FILE_COMPRESS(JournalFile *f) {
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         assert(f);
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         return f->compress_xz || f->compress_lz4;
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 }
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+
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+int journal_file_map_data_hash_table(JournalFile *f);
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+int journal_file_map_field_hash_table(JournalFile *f);
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diff --git a/src/journal/journal-verify.c b/src/journal/journal-verify.c
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index 983217c1bc..d2d5c400c1 100644
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--- a/src/journal/journal-verify.c
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+++ b/src/journal/journal-verify.c
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@@ -590,6 +590,13 @@ static int verify_hash_table(
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         assert(last_usec);
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         n = le64toh(f->header->data_hash_table_size) / sizeof(HashItem);
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+        if (n <= 0)
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+                return 0;
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+
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+        r = journal_file_map_data_hash_table(f);
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+        if (r < 0)
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+                return log_error_errno(r, "Failed to map data hash table: %m");
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+
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         for (i = 0; i < n; i++) {
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                 uint64_t last = 0, p;
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@@ -647,6 +654,13 @@ static int data_object_in_hash_table(JournalFile *f, uint64_t hash, uint64_t p)
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         assert(f);
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         n = le64toh(f->header->data_hash_table_size) / sizeof(HashItem);
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+        if (n <= 0)
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+                return 0;
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+
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+        r = journal_file_map_data_hash_table(f);
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+        if (r < 0)
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+                return log_error_errno(r, "Failed to map data hash table: %m");
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+
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         h = hash % n;
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         q = le64toh(f->data_hash_table[h].head_hash_offset);