fdstream: Implement sparse stream

Basically, what is needed here is to introduce new message type
for the messages passed between the event loop callbacks and the
worker thread that does all the I/O. The idea is that instead of
a queue of read buffers we will have a queue where "hole of size
X" messages appear. That way the event loop callbacks can just
check the head of the queue and see if the worker thread is in
data or a hole section and how long the section is.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

src/storage/storage_util.c

@@ -2427,7 +2427,7 @@ virStorageBackendVolUploadLocal(virConnectPtr conn ATTRIBUTE_UNUSED,
     /* Not using O_CREAT because the file is required to already exist at
      * this point */
     ret = virFDStreamOpenBlockDevice(stream, target_path,
-                                     offset, len, O_WRONLY);
+                                     offset, len, false, O_WRONLY);
 
  cleanup:
     VIR_FREE(path);
@@ -2465,7 +2465,7 @@ virStorageBackendVolDownloadLocal(virConnectPtr conn ATTRIBUTE_UNUSED,
     }
 
     ret = virFDStreamOpenBlockDevice(stream, target_path,
-                                     offset, len, O_RDONLY);
+                                     offset, len, false, O_RDONLY);
 
  cleanup:
     VIR_FREE(path);

src/util/virfdstream.c

@@ -51,6 +51,7 @@ VIR_LOG_INIT("fdstream");
 
 typedef enum {
     VIR_FDSTREAM_MSG_TYPE_DATA,
+    VIR_FDSTREAM_MSG_TYPE_HOLE,
 } virFDStreamMsgType;
 
 typedef struct _virFDStreamMsg virFDStreamMsg;
@@ -66,6 +67,9 @@ struct _virFDStreamMsg {
             size_t len;
             size_t offset;
         } data;
+        struct {
+            long long len;
+        } hole;
     } stream;
 };
 
@@ -198,6 +202,9 @@ virFDStreamMsgFree(virFDStreamMsgPtr msg)
     case VIR_FDSTREAM_MSG_TYPE_DATA:
         VIR_FREE(msg->stream.data.buf);
         break;
+    case VIR_FDSTREAM_MSG_TYPE_HOLE:
+        /* nada */
+        break;
     }
 
     VIR_FREE(msg);
@@ -385,6 +392,7 @@ struct _virFDStreamThreadData {
     virStreamPtr st;
     size_t length;
     bool doRead;
+    bool sparse;
     int fdin;
     char *fdinname;
     int fdout;
@@ -407,19 +415,50 @@ virFDStreamThreadDataFree(virFDStreamThreadDataPtr data)
 
 static ssize_t
 virFDStreamThreadDoRead(virFDStreamDataPtr fdst,
+                        bool sparse,
                         const int fdin,
                         const int fdout,
                         const char *fdinname,
                         const char *fdoutname,
+                        size_t *dataLen,
                         size_t buflen)
 {
     virFDStreamMsgPtr msg = NULL;
+    int inData = 0;
+    long long sectionLen = 0;
     char *buf = NULL;
     ssize_t got;
 
+    if (sparse && *dataLen == 0) {
+        if (virFileInData(fdin, &inData, &sectionLen) < 0)
+            goto error;
+
+        if (inData)
+            *dataLen = sectionLen;
+    }
+
     if (VIR_ALLOC(msg) < 0)
         goto error;
 
+    if (sparse && *dataLen == 0) {
+        msg->type = VIR_FDSTREAM_MSG_TYPE_HOLE;
+        msg->stream.hole.len = sectionLen;
+        got = sectionLen;
+
+        /* HACK: The message queue is one directional. So caller
+         * cannot make us skip the hole. Do that for them instead. */
+        if (sectionLen &&
+            lseek(fdin, sectionLen, SEEK_CUR) == (off_t) -1) {
+            virReportSystemError(errno,
+                                 _("unable to seek in %s"),
+                                 fdinname);
+            goto error;
+        }
+    } else {
+        if (sparse &&
+            buflen > *dataLen)
+            buflen = *dataLen;
+
         if (VIR_ALLOC_N(buf, buflen) < 0)
             goto error;
 
@@ -434,6 +473,9 @@ virFDStreamThreadDoRead(virFDStreamDataPtr fdst,
         msg->stream.data.buf = buf;
         msg->stream.data.len = got;
         buf = NULL;
+        if (sparse)
+            *dataLen -= got;
+    }
 
     virFDStreamMsgQueuePush(fdst, msg, fdout, fdoutname);
     msg = NULL;
@@ -449,6 +491,7 @@ virFDStreamThreadDoRead(virFDStreamDataPtr fdst,
 
 static ssize_t
 virFDStreamThreadDoWrite(virFDStreamDataPtr fdst,
+                         bool sparse,
                          const int fdin,
                          const int fdout,
                          const char *fdinname,
@@ -456,6 +499,7 @@ virFDStreamThreadDoWrite(virFDStreamDataPtr fdst,
 {
     ssize_t got = 0;
     virFDStreamMsgPtr msg = fdst->msg;
+    off_t off;
     bool pop = false;
 
     switch (msg->type) {
@@ -474,6 +518,32 @@ virFDStreamThreadDoWrite(virFDStreamDataPtr fdst,
 
         pop = msg->stream.data.offset == msg->stream.data.len;
         break;
+
+    case VIR_FDSTREAM_MSG_TYPE_HOLE:
+        if (!sparse) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("unexpected stream hole"));
+            return -1;
+        }
+
+        got = msg->stream.hole.len;
+        off = lseek(fdout, got, SEEK_CUR);
+        if (off == (off_t) -1) {
+            virReportSystemError(errno,
+                                 _("unable to seek in %s"),
+                                 fdoutname);
+            return -1;
+        }
+
+        if (ftruncate(fdout, off) < 0) {
+            virReportSystemError(errno,
+                                 _("unable to truncate %s"),
+                                 fdoutname);
+            return -1;
+        }
+
+        pop = true;
+        break;
     }
 
     if (pop) {
@@ -491,6 +561,7 @@ virFDStreamThread(void *opaque)
     virFDStreamThreadDataPtr data = opaque;
     virStreamPtr st = data->st;
     size_t length = data->length;
+    bool sparse = data->sparse;
     int fdin = data->fdin;
     char *fdinname = data->fdinname;
     int fdout = data->fdout;
@@ -499,6 +570,7 @@ virFDStreamThread(void *opaque)
     bool doRead = fdst->threadDoRead;
     size_t buflen = 256 * 1024;
     size_t total = 0;
+    size_t dataLen = 0;
 
     virObjectRef(fdst);
     virObjectLock(fdst);
@@ -533,12 +605,12 @@ virFDStreamThread(void *opaque)
         }
 
         if (doRead)
-            got = virFDStreamThreadDoRead(fdst,
+            got = virFDStreamThreadDoRead(fdst, sparse,
                                           fdin, fdout,
                                           fdinname, fdoutname,
-                                          buflen);
+                                          &dataLen, buflen);
         else
-            got = virFDStreamThreadDoWrite(fdst,
+            got = virFDStreamThreadDoWrite(fdst, sparse,
                                            fdin, fdout,
                                            fdinname, fdoutname);
 
@@ -809,6 +881,14 @@ static int virFDStreamRead(virStreamPtr st, char *bytes, size_t nbytes)
             }
         }
 
+        /* Shortcut, if the stream is in the trailing hole,
+         * return 0 immediately. */
+        if (msg->type == VIR_FDSTREAM_MSG_TYPE_HOLE &&
+            msg->stream.hole.len == 0) {
+            ret = 0;
+            goto cleanup;
+        }
+
         if (msg->type != VIR_FDSTREAM_MSG_TYPE_DATA) {
             /* Nope, nope, I'm outta here */
             virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -859,11 +939,124 @@ static int virFDStreamRead(virStreamPtr st, char *bytes, size_t nbytes)
 }
 
 
+static int
+virFDStreamSendHole(virStreamPtr st,
+                    long long length,
+                    unsigned int flags)
+{
+    virFDStreamDataPtr fdst = st->privateData;
+    virFDStreamMsgPtr msg = NULL;
+    off_t off;
+    int ret = -1;
+
+    virCheckFlags(0, -1);
+
+    virObjectLock(fdst);
+    if (fdst->length) {
+        if (length > fdst->length - fdst->offset)
+            length = fdst->length - fdst->offset;
+        fdst->offset += length;
+    }
+
+    if (fdst->thread) {
+        /* Things are a bit complicated here. If FDStream is in a
+         * read mode, then if the message at the queue head is
+         * HOLE, just pop it. The thread has lseek()-ed anyway.
+         * However, if the FDStream is in write mode, then tell
+         * the thread to do the lseek() for us. Under no
+         * circumstances we can do the lseek() ourselves here. We
+         * might mess up file position for the thread. */
+        if (fdst->threadDoRead) {
+            msg = fdst->msg;
+            if (msg->type != VIR_FDSTREAM_MSG_TYPE_HOLE) {
+                virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                               _("Invalid stream hole"));
+                goto cleanup;
+            }
+
+            virFDStreamMsgQueuePop(fdst, fdst->fd, "pipe");
+        } else {
+            if (VIR_ALLOC(msg) < 0)
+                goto cleanup;
+
+            msg->type = VIR_FDSTREAM_MSG_TYPE_HOLE;
+            msg->stream.hole.len = length;
+            virFDStreamMsgQueuePush(fdst, msg, fdst->fd, "pipe");
+            msg = NULL;
+        }
+    } else {
+        off = lseek(fdst->fd, length, SEEK_CUR);
+        if (off == (off_t) -1) {
+            virReportSystemError(errno, "%s",
+                                 _("unable to seek"));
+            goto cleanup;
+        }
+
+        if (ftruncate(fdst->fd, off) < 0) {
+            virReportSystemError(errno, "%s",
+                                 _("unable to truncate"));
+            goto cleanup;
+        }
+    }
+
+    ret = 0;
+ cleanup:
+    virObjectUnlock(fdst);
+    virFDStreamMsgFree(msg);
+    return ret;
+}
+
+
+static int
+virFDStreamInData(virStreamPtr st,
+                  int *inData,
+                  long long *length)
+{
+    virFDStreamDataPtr fdst = st->privateData;
+    int ret = -1;
+
+    virObjectLock(fdst);
+
+    if (fdst->thread) {
+        virFDStreamMsgPtr msg;
+
+        while (!(msg = fdst->msg)) {
+            if (fdst->threadQuit) {
+                *inData = *length = 0;
+                ret = 0;
+                goto cleanup;
+            } else {
+                virObjectUnlock(fdst);
+                virCondSignal(&fdst->threadCond);
+                virObjectLock(fdst);
+            }
+        }
+
+        if (msg->type == VIR_FDSTREAM_MSG_TYPE_DATA) {
+            *inData = 1;
+            *length = msg->stream.data.len - msg->stream.data.offset;
+        } else {
+            *inData = 0;
+            *length = msg->stream.hole.len;
+        }
+        ret = 0;
+    } else {
+        ret = virFileInData(fdst->fd, inData, length);
+    }
+
+ cleanup:
+    virObjectUnlock(fdst);
+    return ret;
+}
+
+
 static virStreamDriver virFDStreamDrv = {
     .streamSend = virFDStreamWrite,
     .streamRecv = virFDStreamRead,
     .streamFinish = virFDStreamClose,
     .streamAbort = virFDStreamAbort,
+    .streamSendHole = virFDStreamSendHole,
+    .streamInData = virFDStreamInData,
     .streamEventAddCallback = virFDStreamAddCallback,
     .streamEventUpdateCallback = virFDStreamUpdateCallback,
     .streamEventRemoveCallback = virFDStreamRemoveCallback
@@ -1004,7 +1197,8 @@ virFDStreamOpenFileInternal(virStreamPtr st,
                             unsigned long long length,
                             int oflags,
                             int mode,
-                            bool forceIOHelper)
+                            bool forceIOHelper,
+                            bool sparse)
 {
     int fd = -1;
     int pipefds[2] = { -1, -1 };
@@ -1071,6 +1265,7 @@ virFDStreamOpenFileInternal(virStreamPtr st,
 
         threadData->st = virObjectRef(st);
         threadData->length = length;
+        threadData->sparse = sparse;
 
         if ((oflags & O_ACCMODE) == O_RDONLY) {
             threadData->fdin = fd;
@@ -1120,7 +1315,7 @@ int virFDStreamOpenFile(virStreamPtr st,
     }
     return virFDStreamOpenFileInternal(st, path,
                                        offset, length,
-                                       oflags, 0, false);
+                                       oflags, 0, false, false);
 }
 
 int virFDStreamCreateFile(virStreamPtr st,
@@ -1133,7 +1328,7 @@ int virFDStreamCreateFile(virStreamPtr st,
     return virFDStreamOpenFileInternal(st, path,
                                        offset, length,
                                        oflags | O_CREAT, mode,
-                                       false);
+                                       false, false);
 }
 
 #ifdef HAVE_CFMAKERAW
@@ -1149,7 +1344,7 @@ int virFDStreamOpenPTY(virStreamPtr st,
     if (virFDStreamOpenFileInternal(st, path,
                                     offset, length,
                                     oflags | O_CREAT, 0,
-                                    false) < 0)
+                                    false, false) < 0)
         return -1;
 
     fdst = st->privateData;
@@ -1186,7 +1381,7 @@ int virFDStreamOpenPTY(virStreamPtr st,
     return virFDStreamOpenFileInternal(st, path,
                                        offset, length,
                                        oflags | O_CREAT, 0,
-                                       false);
+                                       false, false);
 }
 #endif /* !HAVE_CFMAKERAW */
 
@@ -1194,11 +1389,12 @@ int virFDStreamOpenBlockDevice(virStreamPtr st,
                                const char *path,
                                unsigned long long offset,
                                unsigned long long length,
+                               bool sparse,
                                int oflags)
 {
     return virFDStreamOpenFileInternal(st, path,
                                        offset, length,
-                                       oflags, 0, true);
+                                       oflags, 0, true, sparse);
 }
 
 int virFDStreamSetInternalCloseCb(virStreamPtr st,

src/util/virfdstream.h

@@ -59,6 +59,7 @@ int virFDStreamOpenBlockDevice(virStreamPtr st,
                                const char *path,
                                unsigned long long offset,
                                unsigned long long length,
+                               bool sparse,
                                int oflags);
 
 int virFDStreamSetInternalCloseCb(virStreamPtr st,