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+Date: Sat, 23 Aug 2014 20:57:40 -0400\r
+From: Austin Clements <amdragon@MIT.EDU>\r
+To: Jani Nikula <jani@nikula.org>\r
+Subject: Re: [PATCH v3 04/13] lib: Database version 3: Introduce fine-grained\r
+ "features"\r
+Message-ID: <20140824005740.GM3015@mit.edu>\r
+References: <1406859003-11561-1-git-send-email-amdragon@mit.edu>\r
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+\r
+Quoth Jani Nikula on Aug 23 at 7:02 pm:\r
+> On Fri, 01 Aug 2014, Austin Clements <amdragon@MIT.EDU> wrote:\r
+> > Previously, our database schema was versioned by a single number.\r
+> > Each database schema change had to occur "atomically" in Notmuch's\r
+> > development history: before some commit, Notmuch used version N, after\r
+> > that commit, it used version N+1. Hence, each new schema version\r
+> > could introduce only one change, the task of developing a schema\r
+> > change fell on a single person, and it all had to happen and be\r
+> > perfect in a single commit series. This made introducing a new schema\r
+> > version hard. We've seen only two schema changes in the history of\r
+> > Notmuch.\r
+> >\r
+> > This commit introduces database schema version 3; hopefully the last\r
+> > schema version we'll need for a while. With this version, we switch\r
+> > from a single version number to "features": a set of named,\r
+> > independent aspects of the database schema.\r
+> >\r
+> > Features should make backwards compatibility easier. For many things,\r
+> > it should be easy to support databases both with and without a\r
+> > feature, which will allow us to make upgrades optional and will enable\r
+> > "unstable" features that can be developed and tested over time.\r
+> >\r
+> > Features also make forwards compatibility easier. The features\r
+> > recorded in a database include "compatibility flags," which can\r
+> > indicate to an older version of Notmuch when it must support a given\r
+> > feature to open the database for read or for write. This lets us\r
+> > replace the old vague "I don't recognize this version, so something\r
+> > might go wrong, but I promise to try my best" warnings upon opening a\r
+> > database with an unknown version with precise errors. If a database\r
+> > is safe to open for read/write despite unknown features, an older\r
+> > version will know that and issue no message at all. If the database\r
+> > is not safe to open for read/write because of unknown features, an\r
+> > older version will know that, too, and can tell the user exactly which\r
+> > required features it lacks support for.\r
+> \r
+> I agree with the change overall; it might be useful to have another set\r
+> of eyes on the patch though.\r
+> \r
+> > ---\r
+> > lib/database-private.h | 57 ++++++++++++++-\r
+> > lib/database.cc | 190 ++++++++++++++++++++++++++++++++++++++++---------\r
+> > 2 files changed, 213 insertions(+), 34 deletions(-)\r
+> >\r
+> > diff --git a/lib/database-private.h b/lib/database-private.h\r
+> > index d3e65fd..2ffab33 100644\r
+> > --- a/lib/database-private.h\r
+> > +++ b/lib/database-private.h\r
+> > @@ -41,11 +41,15 @@ struct _notmuch_database {\r
+> > \r
+> > char *path;\r
+> > \r
+> > - notmuch_bool_t needs_upgrade;\r
+> > notmuch_database_mode_t mode;\r
+> > int atomic_nesting;\r
+> > Xapian::Database *xapian_db;\r
+> > \r
+> > + /* Bit mask of features used by this database. Features are\r
+> > + * named, independent aspects of the database schema. This is a\r
+> > + * bitwise-OR of NOTMUCH_FEATURE_* values (below). */\r
+> > + unsigned int features;\r
+> > +\r
+> > unsigned int last_doc_id;\r
+> > uint64_t last_thread_id;\r
+> > \r
+> > @@ -55,6 +59,57 @@ struct _notmuch_database {\r
+> > Xapian::ValueRangeProcessor *date_range_processor;\r
+> > };\r
+> > \r
+> > +/* Bit masks for _notmuch_database::features. */\r
+> > +enum {\r
+> > + /* If set, file names are stored in "file-direntry" terms. If\r
+> > + * unset, file names are stored in document data.\r
+> > + *\r
+> > + * Introduced: version 1. Implementation support: both for read;\r
+> > + * required for write. */\r
+> \r
+> Maybe I'm dense, but the implementation support comments could be\r
+> clearer.\r
+\r
+No, this was too terse. The intent was to state what the current\r
+library implementation supports: e.g., the current implementation\r
+supports reading from databases both with and without\r
+NOTMUCH_FEATURE_FILE_TERMS, but if you attempt to write a database\r
+without this feature, some operations may return\r
+NOTMUCH_STATUS_UPGRADE_REQUIRED (introduced in a later patch).\r
+\r
+I wonder, though, if the "implementation support" bits should just be\r
+omitted. These comments are inevitably going to get out of sync with\r
+the real implementation, and in this case an incorrect comment may be\r
+worse than no comment. I could put a comment over the whole enum\r
+giving a more general description:\r
+\r
+/* Bit masks for _notmuch_database::features. Features are named,\r
+ * independent aspects of the database schema.\r
+ *\r
+ * A database stores the set of features that it "uses" (implicitly\r
+ * before database version 3 and explicitly as of version 3).\r
+ *\r
+ * A given library version will "recognize" a particular set of\r
+ * features; if a database uses a feature that the library does not\r
+ * recognize, the library will refuse to open it. It is assumed the\r
+ * set of recognized features grows monotonically over time. A\r
+ * library version will "implement" some subset of the recognized\r
+ * features: some operations may require that the database use (or not\r
+ * use) some feature, while other operations may support both\r
+ * databases that use and that don't use some feature.\r
+ *\r
+ * On disk, the database stores string names for these features (see\r
+ * the feature_names array). These enum bit values are never\r
+ * persisted to disk and may change freely.\r
+ */\r
+\r
+> > + NOTMUCH_FEATURE_FILE_TERMS = 1 << 0,\r
+> > +\r
+> > + /* If set, directory timestamps are stored in documents with\r
+> > + * XDIRECTORY terms and relative paths. If unset, directory\r
+> > + * timestamps are stored in documents with XTIMESTAMP terms and\r
+> > + * absolute paths.\r
+> > + *\r
+> > + * Introduced: version 1. Implementation support: required. */\r
+> > + NOTMUCH_FEATURE_DIRECTORY_DOCS = 1 << 1,\r
+> > +\r
+> > + /* If set, the from, subject, and message-id headers are stored in\r
+> > + * message document values. If unset, message documents *may*\r
+> > + * have these values, but if the value is empty, it must be\r
+> > + * retrieved from the message file.\r
+> > + *\r
+> > + * Introduced: optional in version 1, required as of version 3.\r
+> > + * Implementation support: both.\r
+> > + */\r
+> > + NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES = 1 << 2,\r
+> > +\r
+> > + /* If set, folder terms are boolean and path terms exist. If\r
+> > + * unset, folder terms are probabilistic and stemmed and path\r
+> > + * terms do not exist.\r
+> > + *\r
+> > + * Introduced: version 2. Implementation support: required. */\r
+> > + NOTMUCH_FEATURE_BOOL_FOLDER = 1 << 3,\r
+> > +};\r
+> > +\r
+> > +/* Prior to database version 3, features were implied by the database\r
+> > + * version number, so hard-code them for earlier versions. */\r
+> > +#define NOTMUCH_FEATURES_V0 (0)\r
+> > +#define NOTMUCH_FEATURES_V1 (NOTMUCH_FEATURES_V0 | NOTMUCH_FEATURE_FILE_TERMS | \\r
+> > + NOTMUCH_FEATURE_DIRECTORY_DOCS)\r
+> > +#define NOTMUCH_FEATURES_V2 (NOTMUCH_FEATURES_V1 | NOTMUCH_FEATURE_BOOL_FOLDER)\r
+> > +\r
+> > +/* Current database features. If any of these are missing from a\r
+> > + * database, request an upgrade.\r
+> > + * NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES is not included because\r
+> > + * upgrade doesn't currently introduce the feature (though brand new\r
+> > + * databases will have it). */\r
+> > +#define NOTMUCH_FEATURES_CURRENT \\r
+> > + (NOTMUCH_FEATURE_FILE_TERMS | NOTMUCH_FEATURE_DIRECTORY_DOCS | \\r
+> > + NOTMUCH_FEATURE_BOOL_FOLDER)\r
+> > +\r
+> > /* Return the list of terms from the given iterator matching a prefix.\r
+> > * The prefix will be stripped from the strings in the returned list.\r
+> > * The list will be allocated using ctx as the talloc context.\r
+> > diff --git a/lib/database.cc b/lib/database.cc\r
+> > index 45c4260..29a56db 100644\r
+> > --- a/lib/database.cc\r
+> > +++ b/lib/database.cc\r
+> > @@ -20,6 +20,7 @@\r
+> > \r
+> > #include "database-private.h"\r
+> > #include "parse-time-vrp.h"\r
+> > +#include "string-util.h"\r
+> > \r
+> > #include <iostream>\r
+> > \r
+> > @@ -42,7 +43,7 @@ typedef struct {\r
+> > const char *prefix;\r
+> > } prefix_t;\r
+> > \r
+> > -#define NOTMUCH_DATABASE_VERSION 2\r
+> > +#define NOTMUCH_DATABASE_VERSION 3\r
+> > \r
+> > #define STRINGIFY(s) _SUB_STRINGIFY(s)\r
+> > #define _SUB_STRINGIFY(s) #s\r
+> > @@ -151,6 +152,17 @@ typedef struct {\r
+> > * changes are made to the database (such as by\r
+> > * indexing new fields).\r
+> > *\r
+> > + * features The set of features supported by this\r
+> > + * database. This consists of a set of\r
+> > + * '\n'-separated lines, where each is a feature\r
+> > + * name, a '\t', and compatibility flags. If the\r
+> > + * compatibility flags contain 'w', then the\r
+> > + * opener must support this feature to safely\r
+> > + * write this database. If the compatibility\r
+> > + * flags contain 'r', then the opener must\r
+> > + * support this feature to read this database.\r
+> > + * Introduced in database version 3.\r
+> > + *\r
+> > * last_thread_id The last thread ID generated. This is stored\r
+> > * as a 16-byte hexadecimal ASCII representation\r
+> > * of a 64-bit unsigned integer. The first ID\r
+> > @@ -251,6 +263,25 @@ _find_prefix (const char *name)\r
+> > return "";\r
+> > }\r
+> > \r
+> > +static const struct\r
+> > +{\r
+> \r
+> Brace should be at the end of the previous line.\r
+\r
+Fixed.\r
+\r
+> > + /* NOTMUCH_FEATURE_* value. */\r
+> > + unsigned int value;\r
+> > + /* Feature name as it appears in the database. This name should\r
+> > + * be appropriate for displaying to the user if an older version\r
+> > + * of notmuch doesn't support this feature. */\r
+> > + const char *name;\r
+> > + /* Compatibility flags when this feature is declared. */\r
+> > + const char *flags;\r
+> > +} feature_names[] = {\r
+> > + {NOTMUCH_FEATURE_FILE_TERMS, "multiple paths per message", "rw"},\r
+> > + {NOTMUCH_FEATURE_DIRECTORY_DOCS, "relative directory paths", "rw"},\r
+> > + /* Header values are not required for reading a database because a\r
+> > + * reader can just refer to the message file. */\r
+> > + {NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES, "from/subject/message-ID in database", "w"},\r
+> > + {NOTMUCH_FEATURE_BOOL_FOLDER, "exact folder:/path: search", "rw"},\r
+> \r
+> Spaces missing after the opening braces and before the closing braces.\r
+\r
+Fixed. I also wrapped all of the entries between the enum name and\r
+the string name since one of the lines was already too long and this\r
+pushed two more over.\r
+\r
+> > +};\r
+> > +\r
+> > const char *\r
+> > notmuch_status_to_string (notmuch_status_t status)\r
+> > {\r
+> > @@ -591,6 +622,11 @@ notmuch_database_create (const char *path, notmuch_database_t **database)\r
+> > ¬much);\r
+> > if (status)\r
+> > goto DONE;\r
+> > +\r
+> > + /* Upgrade doesn't add this feature to existing databases, but new\r
+> > + * databases have it. */\r
+> > + notmuch->features |= NOTMUCH_FEATURE_FROM_SUBJECT_ID_VALUES;\r
+> > +\r
+> > status = notmuch_database_upgrade (notmuch, NULL, NULL);\r
+> > if (status) {\r
+> > notmuch_database_close(notmuch);\r
+> > @@ -619,6 +655,80 @@ _notmuch_database_ensure_writable (notmuch_database_t *notmuch)\r
+> > return NOTMUCH_STATUS_SUCCESS;\r
+> > }\r
+> > \r
+> > +/* Parse a database features string from the given database version.\r
+> > + *\r
+> > + * For version < 3, this ignores the features string and returns a\r
+> > + * hard-coded set of features.\r
+> > + *\r
+> > + * If there are unrecognized features that are required to open the\r
+> > + * database in mode (which should be 'r' or 'w'), return a\r
+> > + * comma-separated list of unrecognized but required features in\r
+> > + * *incompat_out, which will be allocated from ctx.\r
+> \r
+> Please describe the actual return value.\r
+\r
+Fixed. I also gave the enum type a name (in response to David's\r
+review) and used it here, so this is more self-documenting.\r
+\r
+> > + */\r
+> > +static unsigned int\r
+> > +_parse_features (const void *ctx, const char *features, unsigned int version,\r
+> > + char mode, char **incompat_out)\r
+> > +{\r
+> > + unsigned int res = 0, namelen, i;\r
+> > + size_t llen = 0;\r
+> > + const char *flags;\r
+> > +\r
+> > + /* Prior to database version 3, features were implied by the\r
+> > + * version number. */\r
+> > + if (version == 0)\r
+> > + return NOTMUCH_FEATURES_V0;\r
+> > + else if (version == 1)\r
+> > + return NOTMUCH_FEATURES_V1;\r
+> > + else if (version == 2)\r
+> > + return NOTMUCH_FEATURES_V2;\r
+> > +\r
+> > + /* Parse the features string */\r
+> > + while ((features = strtok_len_c (features + llen, "\n", &llen)) != NULL) {\r
+> > + flags = strchr (features, '\t');\r
+> > + if (! flags || flags > features + llen)\r
+> > + continue;\r
+> > + namelen = flags - features;\r
+> > +\r
+> > + for (i = 0; i < ARRAY_SIZE (feature_names); ++i) {\r
+> > + if (strlen (feature_names[i].name) == namelen &&\r
+> > + strncmp (feature_names[i].name, features, namelen) == 0) {\r
+> > + res |= feature_names[i].value;\r
+> > + break;\r
+> > + }\r
+> > + }\r
+> > +\r
+> > + if (i == ARRAY_SIZE (feature_names)) {\r
+> > + /* Unrecognized feature */\r
+> > + const char *have = strchr (flags, mode);\r
+> > + if (have && have < features + llen) {\r
+> > + /* This feature is required to access this database in\r
+> > + * 'mode', but we don't understand it. */\r
+> > + if (! *incompat_out)\r
+> > + *incompat_out = talloc_strdup (ctx, "");\r
+> > + *incompat_out = talloc_asprintf_append_buffer (\r
+> > + *incompat_out, "%s%.*s", **incompat_out ? ", " : "",\r
+> > + namelen, features);\r
+> \r
+> Do we intend the lib user to be able to parse the features? Perhaps we\r
+> should use '\n' as separator here too? (Although looks like *currently*\r
+> this is only for printing the message from within the lib.)\r
+\r
+I'd intended this only for user presentation. I updated the comment\r
+to mention this. If it turns out we need this information in a\r
+computer-friendly form in the future, it should be easy to add.\r
+\r
+> > + }\r
+> > + }\r
+> > + }\r
+> > +\r
+> > + return res;\r
+> > +}\r
+> > +\r
+> > +static char *\r
+> > +_print_features (const void *ctx, unsigned int features)\r
+> > +{\r
+> > + unsigned int i;\r
+> > + char *res = talloc_strdup (ctx, "");\r
+> > +\r
+> > + for (i = 0; i < ARRAY_SIZE (feature_names); ++i)\r
+> > + if (features & feature_names[i].value)\r
+> > + res = talloc_asprintf_append_buffer (\r
+> > + res, "%s\t%s\n", feature_names[i].name, feature_names[i].flags);\r
+> > +\r
+> > + return res;\r
+> > +}\r
+> > +\r
+> > notmuch_status_t\r
+> > notmuch_database_open (const char *path,\r
+> > notmuch_database_mode_t mode,\r
+> > @@ -627,7 +737,7 @@ notmuch_database_open (const char *path,\r
+> > notmuch_status_t status = NOTMUCH_STATUS_SUCCESS;\r
+> > void *local = talloc_new (NULL);\r
+> > notmuch_database_t *notmuch = NULL;\r
+> > - char *notmuch_path, *xapian_path;\r
+> > + char *notmuch_path, *xapian_path, *incompat_features;\r
+> > struct stat st;\r
+> > int err;\r
+> > unsigned int i, version;\r
+> > @@ -677,7 +787,6 @@ notmuch_database_open (const char *path,\r
+> > if (notmuch->path[strlen (notmuch->path) - 1] == '/')\r
+> > notmuch->path[strlen (notmuch->path) - 1] = '\0';\r
+> > \r
+> > - notmuch->needs_upgrade = FALSE;\r
+> > notmuch->mode = mode;\r
+> > notmuch->atomic_nesting = 0;\r
+> > try {\r
+> > @@ -686,37 +795,44 @@ notmuch_database_open (const char *path,\r
+> > if (mode == NOTMUCH_DATABASE_MODE_READ_WRITE) {\r
+> > notmuch->xapian_db = new Xapian::WritableDatabase (xapian_path,\r
+> > Xapian::DB_CREATE_OR_OPEN);\r
+> > - version = notmuch_database_get_version (notmuch);\r
+> > -\r
+> > - if (version > NOTMUCH_DATABASE_VERSION) {\r
+> > - fprintf (stderr,\r
+> > - "Error: Notmuch database at %s\n"\r
+> > - " has a newer database format version (%u) than supported by this\n"\r
+> > - " version of notmuch (%u). Refusing to open this database in\n"\r
+> > - " read-write mode.\n",\r
+> > - notmuch_path, version, NOTMUCH_DATABASE_VERSION);\r
+> > - notmuch->mode = NOTMUCH_DATABASE_MODE_READ_ONLY;\r
+> > - notmuch_database_destroy (notmuch);\r
+> > - notmuch = NULL;\r
+> > - status = NOTMUCH_STATUS_FILE_ERROR;\r
+> > - goto DONE;\r
+> > - }\r
+> > -\r
+> > - if (version < NOTMUCH_DATABASE_VERSION)\r
+> > - notmuch->needs_upgrade = TRUE;\r
+> > } else {\r
+> > notmuch->xapian_db = new Xapian::Database (xapian_path);\r
+> > - version = notmuch_database_get_version (notmuch);\r
+> > - if (version > NOTMUCH_DATABASE_VERSION)\r
+> > - {\r
+> > - fprintf (stderr,\r
+> > - "Warning: Notmuch database at %s\n"\r
+> > - " has a newer database format version (%u) than supported by this\n"\r
+> > - " version of notmuch (%u). Some operations may behave incorrectly,\n"\r
+> > - " (but the database will not be harmed since it is being opened\n"\r
+> > - " in read-only mode).\n",\r
+> > - notmuch_path, version, NOTMUCH_DATABASE_VERSION);\r
+> > - }\r
+> > + }\r
+> > +\r
+> > + /* Check version. As of database version 3, we represent\r
+> > + * changes in terms of features, so assume a version bump\r
+> > + * means a dramatically incompatible change. */\r
+> > + version = notmuch_database_get_version (notmuch);\r
+> > + if (version > NOTMUCH_DATABASE_VERSION) {\r
+> > + fprintf (stderr,\r
+> > + "Error: Notmuch database at %s\n"\r
+> > + " has a newer database format version (%u) than supported by this\n"\r
+> > + " version of notmuch (%u).\n",\r
+> > + notmuch_path, version, NOTMUCH_DATABASE_VERSION);\r
+> > + notmuch->mode = NOTMUCH_DATABASE_MODE_READ_ONLY;\r
+> > + notmuch_database_destroy (notmuch);\r
+> > + notmuch = NULL;\r
+> > + status = NOTMUCH_STATUS_FILE_ERROR;\r
+> > + goto DONE;\r
+> > + }\r
+> > +\r
+> > + /* Check features. */\r
+> > + incompat_features = NULL;\r
+> > + notmuch->features = _parse_features (\r
+> > + local, notmuch->xapian_db->get_metadata ("features").c_str (),\r
+> > + version, mode == NOTMUCH_DATABASE_MODE_READ_WRITE ? 'w' : 'r',\r
+> \r
+> Makes me think _parse_features could use notmuch_database_mode_t mode\r
+> instead of char mode. *shrug*.\r
+\r
+In principle there could be other compatibility modes, though I can't\r
+imagine what they would be.\r
+\r
+> > + &incompat_features);\r
+> > + if (incompat_features) {\r
+> > + fprintf (stderr,\r
+> > + "Error: Notmuch database at %s\n"\r
+> > + " requires features (%s)\n"\r
+> > + " not supported by this version of notmuch.\n",\r
+> > + notmuch_path, incompat_features);\r
+> > + notmuch->mode = NOTMUCH_DATABASE_MODE_READ_ONLY;\r
+> > + notmuch_database_destroy (notmuch);\r
+> > + notmuch = NULL;\r
+> > + status = NOTMUCH_STATUS_FILE_ERROR;\r
+> > + goto DONE;\r
+> > }\r
+> > \r
+> > notmuch->last_doc_id = notmuch->xapian_db->get_lastdocid ();\r
+> > @@ -1048,7 +1164,8 @@ notmuch_database_get_version (notmuch_database_t *notmuch)\r
+> > notmuch_bool_t\r
+> > notmuch_database_needs_upgrade (notmuch_database_t *notmuch)\r
+> > {\r
+> > - return notmuch->needs_upgrade;\r
+> > + return notmuch->mode == NOTMUCH_DATABASE_MODE_READ_WRITE &&\r
+> > + (NOTMUCH_FEATURES_CURRENT & ~notmuch->features);\r
+> > }\r
+> \r
+> Am I correct that this does not lead to a database upgrade from v2 to v3\r
+> until we actually change the features?\r
+\r
+Yep, that's true (though new databases will start with v3).\r
+Conveniently, I have a bunch of patches that introduce some new\r
+features pending right behind this series. :)\r
+\r
+> Aside, why don't we return a suitable status code from\r
+> notmuch_database_open when an upgrade is required?\r
+\r
+That may make sense at this point in the series, but later patches\r
+make upgrades no longer "required" and instead enforce database\r
+feature requirements on a per-operation basis. At that point, this\r
+function becomes effectively optional; more "wants_upgrade" than\r
+"needs_upgrade".\r
+\r
+> > static volatile sig_atomic_t do_progress_notify = 0;\r
+> > @@ -1077,6 +1194,7 @@ notmuch_database_upgrade (notmuch_database_t *notmuch,\r
+> > double progress),\r
+> > void *closure)\r
+> > {\r
+> > + void *local = talloc_new (NULL);\r
+> > Xapian::WritableDatabase *db;\r
+> > struct sigaction action;\r
+> > struct itimerval timerval;\r
+> > @@ -1114,6 +1232,10 @@ notmuch_database_upgrade (notmuch_database_t *notmuch,\r
+> > timer_is_active = TRUE;\r
+> > }\r
+> > \r
+> > + /* Set the target features so we write out changes in the desired\r
+> > + * format. */\r
+> > + notmuch->features |= NOTMUCH_FEATURES_CURRENT;\r
+> > +\r
+> > /* Before version 1, each message document had its filename in the\r
+> > * data field. Copy that into the new format by calling\r
+> > * notmuch_message_add_filename.\r
+> > @@ -1226,6 +1348,7 @@ notmuch_database_upgrade (notmuch_database_t *notmuch,\r
+> > notmuch_query_destroy (query);\r
+> > }\r
+> > \r
+> > + db->set_metadata ("features", _print_features (local, notmuch->features));\r
+> > db->set_metadata ("version", STRINGIFY (NOTMUCH_DATABASE_VERSION));\r
+> > db->flush ();\r
+> > \r
+> > @@ -1302,6 +1425,7 @@ notmuch_database_upgrade (notmuch_database_t *notmuch,\r
+> > sigaction (SIGALRM, &action, NULL);\r
+> > }\r
+> > \r
+> > + talloc_free (local);\r
+> > return NOTMUCH_STATUS_SUCCESS;\r
+> > }\r
+> > \r
projects / notmuch-archives.git / commitdiff