All of lore.kernel.org
 help / color / mirror / Atom feed
From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
To: qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <fam@euphon.net>,
	Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
	Wen Congyang <wencongyang2@huawei.com>,
	Xie Changlong <xiechanglong.d@gmail.com>,
	Emanuele Giuseppe Esposito <eesposit@redhat.com>,
	Markus Armbruster <armbru@redhat.com>,
	qemu-devel@nongnu.org, Hanna Reitz <hreitz@redhat.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>, John Snow <jsnow@redhat.com>
Subject: [RFC PATCH 01/15] jobs: add job-common.h
Date: Fri, 29 Oct 2021 12:39:00 -0400	[thread overview]
Message-ID: <20211029163914.4044794-2-eesposit@redhat.com> (raw)
In-Reply-To: <20211029163914.4044794-1-eesposit@redhat.com>

job-common.h contains all struct and common function that currently
are in job.h and will be shared by job-monitor and job-driver in
the next commits.

No functional change intended.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 include/qemu/job-common.h | 300 ++++++++++++++++++++++++++++++++++++++
 include/qemu/job.h        | 271 +---------------------------------
 2 files changed, 301 insertions(+), 270 deletions(-)
 create mode 100644 include/qemu/job-common.h

diff --git a/include/qemu/job-common.h b/include/qemu/job-common.h
new file mode 100644
index 0000000000..c115028e33
--- /dev/null
+++ b/include/qemu/job-common.h
@@ -0,0 +1,300 @@
+/*
+ * Declarations for background jobs
+ *
+ * Copyright (c) 2011 IBM Corp.
+ * Copyright (c) 2012, 2018 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef JOB_COMMON_H
+#define JOB_COMMON_H
+
+#include "qapi/qapi-types-job.h"
+#include "qemu/queue.h"
+#include "qemu/progress_meter.h"
+#include "qemu/coroutine.h"
+#include "block/aio.h"
+
+typedef struct JobDriver JobDriver;
+typedef struct JobTxn JobTxn;
+
+
+/**
+ * Long-running operation.
+ */
+typedef struct Job {
+    /** The ID of the job. May be NULL for internal jobs. */
+    char *id;
+
+    /** The type of this job. */
+    const JobDriver *driver;
+
+    /** Reference count of the block job */
+    int refcnt;
+
+    /** Current state; See @JobStatus for details. */
+    JobStatus status;
+
+    /** AioContext to run the job coroutine in */
+    AioContext *aio_context;
+
+    /**
+     * The coroutine that executes the job.  If not NULL, it is reentered when
+     * busy is false and the job is cancelled.
+     */
+    Coroutine *co;
+
+    /**
+     * Timer that is used by @job_sleep_ns. Accessed under job_mutex (in
+     * job.c).
+     */
+    QEMUTimer sleep_timer;
+
+    /**
+     * Counter for pause request. If non-zero, the block job is either paused,
+     * or if busy == true will pause itself as soon as possible.
+     */
+    int pause_count;
+
+    /**
+     * Set to false by the job while the coroutine has yielded and may be
+     * re-entered by job_enter(). There may still be I/O or event loop activity
+     * pending. Accessed under block_job_mutex (in blockjob.c).
+     *
+     * When the job is deferred to the main loop, busy is true as long as the
+     * bottom half is still pending.
+     */
+    bool busy;
+
+    /**
+     * Set to true by the job while it is in a quiescent state, where
+     * no I/O or event loop activity is pending.
+     */
+    bool paused;
+
+    /**
+     * Set to true if the job is paused by user.  Can be unpaused with the
+     * block-job-resume QMP command.
+     */
+    bool user_paused;
+
+    /**
+     * Set to true if the job should cancel itself.  The flag must
+     * always be tested just before toggling the busy flag from false
+     * to true.  After a job has been cancelled, it should only yield
+     * if #aio_poll will ("sooner or later") reenter the coroutine.
+     */
+    bool cancelled;
+
+    /**
+     * Set to true if the job should abort immediately without waiting
+     * for data to be in sync.
+     */
+    bool force_cancel;
+
+    /** Set to true when the job has deferred work to the main loop. */
+    bool deferred_to_main_loop;
+
+    /** True if this job should automatically finalize itself */
+    bool auto_finalize;
+
+    /** True if this job should automatically dismiss itself */
+    bool auto_dismiss;
+
+    ProgressMeter progress;
+
+    /**
+     * Return code from @run and/or @prepare callback(s).
+     * Not final until the job has reached the CONCLUDED status.
+     * 0 on success, -errno on failure.
+     */
+    int ret;
+
+    /**
+     * Error object for a failed job.
+     * If job->ret is nonzero and an error object was not set, it will be set
+     * to strerror(-job->ret) during job_completed.
+     */
+    Error *err;
+
+    /** The completion function that will be called when the job completes.  */
+    BlockCompletionFunc *cb;
+
+    /** The opaque value that is passed to the completion function.  */
+    void *opaque;
+
+    /** Notifiers called when a cancelled job is finalised */
+    NotifierList on_finalize_cancelled;
+
+    /** Notifiers called when a successfully completed job is finalised */
+    NotifierList on_finalize_completed;
+
+    /** Notifiers called when the job transitions to PENDING */
+    NotifierList on_pending;
+
+    /** Notifiers called when the job transitions to READY */
+    NotifierList on_ready;
+
+    /** Notifiers called when the job coroutine yields or terminates */
+    NotifierList on_idle;
+
+    /** Element of the list of jobs */
+    QLIST_ENTRY(Job) job_list;
+
+    /** Transaction this job is part of */
+    JobTxn *txn;
+
+    /** Element of the list of jobs in a job transaction */
+    QLIST_ENTRY(Job) txn_list;
+} Job;
+
+/**
+ * Callbacks and other information about a Job driver.
+ */
+struct JobDriver {
+
+    /* Fields initialized in struct definition and never changed. */
+
+    /** Derived Job struct size */
+    size_t instance_size;
+
+    /** Enum describing the operation */
+    JobType job_type;
+
+    /*
+     * Functions run without regard to the BQL and may run in any
+     * arbitrary thread. These functions do not need to be thread-safe
+     * because the caller ensures that are invoked from one thread at time.
+     */
+
+    /**
+     * Mandatory: Entrypoint for the Coroutine.
+     *
+     * This callback will be invoked when moving from CREATED to RUNNING.
+     *
+     * If this callback returns nonzero, the job transaction it is part of is
+     * aborted. If it returns zero, the job moves into the WAITING state. If it
+     * is the last job to complete in its transaction, all jobs in the
+     * transaction move from WAITING to PENDING.
+     */
+    int coroutine_fn (*run)(Job *job, Error **errp);
+
+    /**
+     * If the callback is not NULL, it will be invoked when the job transitions
+     * into the paused state.  Paused jobs must not perform any asynchronous
+     * I/O or event loop activity.  This callback is used to quiesce jobs.
+     */
+    void coroutine_fn (*pause)(Job *job);
+
+    /**
+     * If the callback is not NULL, it will be invoked when the job transitions
+     * out of the paused state.  Any asynchronous I/O or event loop activity
+     * should be restarted from this callback.
+     */
+    void coroutine_fn (*resume)(Job *job);
+
+    /*
+     * Global state (GS) API. These functions run under the BQL lock.
+     *
+     * See include/block/block-global-state.h for more information about
+     * the GS API.
+     */
+
+    /**
+     * Called when the job is resumed by the user (i.e. user_paused becomes
+     * false). .user_resume is called before .resume.
+     */
+    void (*user_resume)(Job *job);
+
+    /**
+     * Optional callback for job types whose completion must be triggered
+     * manually.
+     */
+    void (*complete)(Job *job, Error **errp);
+
+    /**
+     * If the callback is not NULL, prepare will be invoked when all the jobs
+     * belonging to the same transaction complete; or upon this job's completion
+     * if it is not in a transaction.
+     *
+     * This callback will not be invoked if the job has already failed.
+     * If it fails, abort and then clean will be called.
+     */
+    int (*prepare)(Job *job);
+
+    /**
+     * If the callback is not NULL, it will be invoked when all the jobs
+     * belonging to the same transaction complete; or upon this job's
+     * completion if it is not in a transaction. Skipped if NULL.
+     *
+     * All jobs will complete with a call to either .commit() or .abort() but
+     * never both.
+     */
+    void (*commit)(Job *job);
+
+    /**
+     * If the callback is not NULL, it will be invoked when any job in the
+     * same transaction fails; or upon this job's failure (due to error or
+     * cancellation) if it is not in a transaction. Skipped if NULL.
+     *
+     * All jobs will complete with a call to either .commit() or .abort() but
+     * never both.
+     */
+    void (*abort)(Job *job);
+
+    /**
+     * If the callback is not NULL, it will be invoked after a call to either
+     * .commit() or .abort(). Regardless of which callback is invoked after
+     * completion, .clean() will always be called, even if the job does not
+     * belong to a transaction group.
+     */
+    void (*clean)(Job *job);
+
+    /**
+     * If the callback is not NULL, it will be invoked in job_cancel_async
+     *
+     * This function must return true if the job will be cancelled
+     * immediately without any further I/O (mandatory if @force is
+     * true), and false otherwise.  This lets the generic job layer
+     * know whether a job has been truly (force-)cancelled, or whether
+     * it is just in a special completion mode (like mirror after
+     * READY).
+     * (If the callback is NULL, the job is assumed to terminate
+     * without I/O.)
+     */
+    bool (*cancel)(Job *job, bool force);
+
+
+    /** Called when the job is freed */
+    void (*free)(Job *job);
+};
+
+typedef enum JobCreateFlags {
+    /* Default behavior */
+    JOB_DEFAULT = 0x00,
+    /* Job is not QMP-created and should not send QMP events */
+    JOB_INTERNAL = 0x01,
+    /* Job requires manual finalize step */
+    JOB_MANUAL_FINALIZE = 0x02,
+    /* Job requires manual dismiss step */
+    JOB_MANUAL_DISMISS = 0x04,
+} JobCreateFlags;
+
+#endif
diff --git a/include/qemu/job.h b/include/qemu/job.h
index 7e9e59f4b8..3cfd79088c 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -26,276 +26,7 @@
 #ifndef JOB_H
 #define JOB_H
 
-#include "qapi/qapi-types-job.h"
-#include "qemu/queue.h"
-#include "qemu/progress_meter.h"
-#include "qemu/coroutine.h"
-#include "block/aio.h"
-
-typedef struct JobDriver JobDriver;
-typedef struct JobTxn JobTxn;
-
-
-/**
- * Long-running operation.
- */
-typedef struct Job {
-    /** The ID of the job. May be NULL for internal jobs. */
-    char *id;
-
-    /** The type of this job. */
-    const JobDriver *driver;
-
-    /** Reference count of the block job */
-    int refcnt;
-
-    /** Current state; See @JobStatus for details. */
-    JobStatus status;
-
-    /** AioContext to run the job coroutine in */
-    AioContext *aio_context;
-
-    /**
-     * The coroutine that executes the job.  If not NULL, it is reentered when
-     * busy is false and the job is cancelled.
-     */
-    Coroutine *co;
-
-    /**
-     * Timer that is used by @job_sleep_ns. Accessed under job_mutex (in
-     * job.c).
-     */
-    QEMUTimer sleep_timer;
-
-    /**
-     * Counter for pause request. If non-zero, the block job is either paused,
-     * or if busy == true will pause itself as soon as possible.
-     */
-    int pause_count;
-
-    /**
-     * Set to false by the job while the coroutine has yielded and may be
-     * re-entered by job_enter(). There may still be I/O or event loop activity
-     * pending. Accessed under block_job_mutex (in blockjob.c).
-     *
-     * When the job is deferred to the main loop, busy is true as long as the
-     * bottom half is still pending.
-     */
-    bool busy;
-
-    /**
-     * Set to true by the job while it is in a quiescent state, where
-     * no I/O or event loop activity is pending.
-     */
-    bool paused;
-
-    /**
-     * Set to true if the job is paused by user.  Can be unpaused with the
-     * block-job-resume QMP command.
-     */
-    bool user_paused;
-
-    /**
-     * Set to true if the job should cancel itself.  The flag must
-     * always be tested just before toggling the busy flag from false
-     * to true.  After a job has been cancelled, it should only yield
-     * if #aio_poll will ("sooner or later") reenter the coroutine.
-     */
-    bool cancelled;
-
-    /**
-     * Set to true if the job should abort immediately without waiting
-     * for data to be in sync.
-     */
-    bool force_cancel;
-
-    /** Set to true when the job has deferred work to the main loop. */
-    bool deferred_to_main_loop;
-
-    /** True if this job should automatically finalize itself */
-    bool auto_finalize;
-
-    /** True if this job should automatically dismiss itself */
-    bool auto_dismiss;
-
-    ProgressMeter progress;
-
-    /**
-     * Return code from @run and/or @prepare callback(s).
-     * Not final until the job has reached the CONCLUDED status.
-     * 0 on success, -errno on failure.
-     */
-    int ret;
-
-    /**
-     * Error object for a failed job.
-     * If job->ret is nonzero and an error object was not set, it will be set
-     * to strerror(-job->ret) during job_completed.
-     */
-    Error *err;
-
-    /** The completion function that will be called when the job completes.  */
-    BlockCompletionFunc *cb;
-
-    /** The opaque value that is passed to the completion function.  */
-    void *opaque;
-
-    /** Notifiers called when a cancelled job is finalised */
-    NotifierList on_finalize_cancelled;
-
-    /** Notifiers called when a successfully completed job is finalised */
-    NotifierList on_finalize_completed;
-
-    /** Notifiers called when the job transitions to PENDING */
-    NotifierList on_pending;
-
-    /** Notifiers called when the job transitions to READY */
-    NotifierList on_ready;
-
-    /** Notifiers called when the job coroutine yields or terminates */
-    NotifierList on_idle;
-
-    /** Element of the list of jobs */
-    QLIST_ENTRY(Job) job_list;
-
-    /** Transaction this job is part of */
-    JobTxn *txn;
-
-    /** Element of the list of jobs in a job transaction */
-    QLIST_ENTRY(Job) txn_list;
-} Job;
-
-/**
- * Callbacks and other information about a Job driver.
- */
-struct JobDriver {
-
-    /* Fields initialized in struct definition and never changed. */
-
-    /** Derived Job struct size */
-    size_t instance_size;
-
-    /** Enum describing the operation */
-    JobType job_type;
-
-    /*
-     * Functions run without regard to the BQL and may run in any
-     * arbitrary thread. These functions do not need to be thread-safe
-     * because the caller ensures that are invoked from one thread at time.
-     */
-
-    /**
-     * Mandatory: Entrypoint for the Coroutine.
-     *
-     * This callback will be invoked when moving from CREATED to RUNNING.
-     *
-     * If this callback returns nonzero, the job transaction it is part of is
-     * aborted. If it returns zero, the job moves into the WAITING state. If it
-     * is the last job to complete in its transaction, all jobs in the
-     * transaction move from WAITING to PENDING.
-     */
-    int coroutine_fn (*run)(Job *job, Error **errp);
-
-    /**
-     * If the callback is not NULL, it will be invoked when the job transitions
-     * into the paused state.  Paused jobs must not perform any asynchronous
-     * I/O or event loop activity.  This callback is used to quiesce jobs.
-     */
-    void coroutine_fn (*pause)(Job *job);
-
-    /**
-     * If the callback is not NULL, it will be invoked when the job transitions
-     * out of the paused state.  Any asynchronous I/O or event loop activity
-     * should be restarted from this callback.
-     */
-    void coroutine_fn (*resume)(Job *job);
-
-    /*
-     * Global state (GS) API. These functions run under the BQL lock.
-     *
-     * See include/block/block-global-state.h for more information about
-     * the GS API.
-     */
-
-    /**
-     * Called when the job is resumed by the user (i.e. user_paused becomes
-     * false). .user_resume is called before .resume.
-     */
-    void (*user_resume)(Job *job);
-
-    /**
-     * Optional callback for job types whose completion must be triggered
-     * manually.
-     */
-    void (*complete)(Job *job, Error **errp);
-
-    /**
-     * If the callback is not NULL, prepare will be invoked when all the jobs
-     * belonging to the same transaction complete; or upon this job's completion
-     * if it is not in a transaction.
-     *
-     * This callback will not be invoked if the job has already failed.
-     * If it fails, abort and then clean will be called.
-     */
-    int (*prepare)(Job *job);
-
-    /**
-     * If the callback is not NULL, it will be invoked when all the jobs
-     * belonging to the same transaction complete; or upon this job's
-     * completion if it is not in a transaction. Skipped if NULL.
-     *
-     * All jobs will complete with a call to either .commit() or .abort() but
-     * never both.
-     */
-    void (*commit)(Job *job);
-
-    /**
-     * If the callback is not NULL, it will be invoked when any job in the
-     * same transaction fails; or upon this job's failure (due to error or
-     * cancellation) if it is not in a transaction. Skipped if NULL.
-     *
-     * All jobs will complete with a call to either .commit() or .abort() but
-     * never both.
-     */
-    void (*abort)(Job *job);
-
-    /**
-     * If the callback is not NULL, it will be invoked after a call to either
-     * .commit() or .abort(). Regardless of which callback is invoked after
-     * completion, .clean() will always be called, even if the job does not
-     * belong to a transaction group.
-     */
-    void (*clean)(Job *job);
-
-    /**
-     * If the callback is not NULL, it will be invoked in job_cancel_async
-     *
-     * This function must return true if the job will be cancelled
-     * immediately without any further I/O (mandatory if @force is
-     * true), and false otherwise.  This lets the generic job layer
-     * know whether a job has been truly (force-)cancelled, or whether
-     * it is just in a special completion mode (like mirror after
-     * READY).
-     * (If the callback is NULL, the job is assumed to terminate
-     * without I/O.)
-     */
-    bool (*cancel)(Job *job, bool force);
-
-
-    /** Called when the job is freed */
-    void (*free)(Job *job);
-};
-
-typedef enum JobCreateFlags {
-    /* Default behavior */
-    JOB_DEFAULT = 0x00,
-    /* Job is not QMP-created and should not send QMP events */
-    JOB_INTERNAL = 0x01,
-    /* Job requires manual finalize step */
-    JOB_MANUAL_FINALIZE = 0x02,
-    /* Job requires manual dismiss step */
-    JOB_MANUAL_DISMISS = 0x04,
-} JobCreateFlags;
+#include "job-common.h"
 
 /**
  * Allocate and return a new job transaction. Jobs can be added to the
-- 
2.27.0



  reply	other threads:[~2021-10-29 16:43 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-29 16:38 [RFC PATCH 00/15] job: replace AioContext lock with job_mutex Emanuele Giuseppe Esposito
2021-10-29 16:39 ` Emanuele Giuseppe Esposito [this message]
2021-11-02 10:07   ` [RFC PATCH 01/15] jobs: add job-common.h Stefan Hajnoczi
2021-10-29 16:39 ` [RFC PATCH 02/15] job.c: make job_lock/unlock public Emanuele Giuseppe Esposito
2021-11-02 10:10   ` Stefan Hajnoczi
2021-10-29 16:39 ` [RFC PATCH 03/15] job-common.h: categorize fields in struct Job Emanuele Giuseppe Esposito
2021-11-02 10:19   ` Stefan Hajnoczi
2021-10-29 16:39 ` [RFC PATCH 04/15] jobs: add job-monitor.h Emanuele Giuseppe Esposito
2021-10-29 16:39 ` [RFC PATCH 05/15] job-monitor.h: define the job monitor API Emanuele Giuseppe Esposito
2021-10-29 16:39 ` [RFC PATCH 06/15] jobs: add job-driver.h Emanuele Giuseppe Esposito
2021-10-29 16:39 ` [RFC PATCH 07/15] job-driver.h: add helper functions Emanuele Giuseppe Esposito
2021-11-02 10:54   ` Vladimir Sementsov-Ogievskiy
2021-10-29 16:39 ` [RFC PATCH 08/15] job.c: minor adjustments in preparation to job-driver Emanuele Giuseppe Esposito
2021-11-02 10:51   ` Vladimir Sementsov-Ogievskiy
2021-10-29 16:39 ` [RFC PATCH 09/15] job.c: move inner aiocontext lock in callbacks Emanuele Giuseppe Esposito
2021-10-29 16:39 ` [RFC PATCH 10/15] aio-wait.h: introduce AIO_WAIT_WHILE_UNLOCKED Emanuele Giuseppe Esposito
2021-10-29 16:39 ` [RFC PATCH 11/15] jobs: remove aiocontext locks since the functions are under BQL Emanuele Giuseppe Esposito
2021-11-02 12:41   ` Vladimir Sementsov-Ogievskiy
2021-11-03 15:56     ` Emanuele Giuseppe Esposito
2021-10-29 16:39 ` [RFC PATCH 12/15] jobs: protect jobs with job_lock/unlock Emanuele Giuseppe Esposito
2021-11-02 12:53   ` Vladimir Sementsov-Ogievskiy
2021-10-29 16:39 ` [RFC PATCH 13/15] jobs: use job locks and helpers also in the unit tests Emanuele Giuseppe Esposito
2021-10-29 16:39 ` [RFC PATCH 14/15] jobs: add missing job locks to replace aiocontext lock Emanuele Giuseppe Esposito
2021-10-29 16:39 ` [RFC PATCH 15/15] jobs: remove all unnecessary AioContext locks Emanuele Giuseppe Esposito
2021-11-02 10:06 ` [RFC PATCH 00/15] job: replace AioContext lock with job_mutex Stefan Hajnoczi
2021-11-02 13:08 ` Vladimir Sementsov-Ogievskiy
2021-11-02 14:13   ` Emanuele Giuseppe Esposito
2021-11-02 14:58     ` Vladimir Sementsov-Ogievskiy

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20211029163914.4044794-2-eesposit@redhat.com \
    --to=eesposit@redhat.com \
    --cc=armbru@redhat.com \
    --cc=fam@euphon.net \
    --cc=hreitz@redhat.com \
    --cc=jsnow@redhat.com \
    --cc=kwolf@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=qemu-block@nongnu.org \
    --cc=qemu-devel@nongnu.org \
    --cc=stefanha@redhat.com \
    --cc=vsementsov@virtuozzo.com \
    --cc=wencongyang2@huawei.com \
    --cc=xiechanglong.d@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.