[Qemu-devel] [PATCH V3] block/nfs: cache allocated filesize for read-only files

[Qemu-devel] [PATCH V3] block/nfs: cache allocated filesize for read-only files

[Peter Lieven]

If the file is readonly its not expected to grow so
save the blocking call to nfs_fstat_async and use
the value saved at connection time. Also important
the monitor (and thus the main loop) will not hang
if block device info is queried and the NFS share
is unresponsive.

Signed-off-by: Peter Lieven <pl@kamp.de>
---
v1->v2: update cache on reopen_prepare [Max]
v2->v3: use cache only if cache.direct=off [Max]

 block/nfs.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/block/nfs.c b/block/nfs.c
index 02eb4e4..887a98e 100644
--- a/block/nfs.c
+++ b/block/nfs.c
@@ -43,6 +43,7 @@ typedef struct NFSClient {
     int events;
     bool has_zero_init;
     AioContext *aio_context;
+    blkcnt_t st_blocks;
 } NFSClient;
 
 typedef struct NFSRPC {
@@ -374,6 +375,7 @@ static int64_t nfs_client_open(NFSClient *client, const char *filename,
     }
 
     ret = DIV_ROUND_UP(st.st_size, BDRV_SECTOR_SIZE);
+    client->st_blocks = st.st_blocks;
     client->has_zero_init = S_ISREG(st.st_mode);
     goto out;
 fail:
@@ -464,6 +466,11 @@ static int64_t nfs_get_allocated_file_size(BlockDriverState *bs)
     NFSRPC task = {0};
     struct stat st;
 
+    if (bdrv_is_read_only(bs) &&
+        !(bs->open_flags & BDRV_O_NOCACHE)) {
+        return client->st_blocks * 512;
+    }
+
     task.st = &st;
     if (nfs_fstat_async(client->context, client->fh, nfs_co_generic_cb,
                         &task) != 0) {
@@ -484,6 +491,34 @@ static int nfs_file_truncate(BlockDriverState *bs, int64_t offset)
     return nfs_ftruncate(client->context, client->fh, offset);
 }
 
+/* Note that this will not re-establish a connection with the NFS server
+ * - it is effectively a NOP.  */
+static int nfs_reopen_prepare(BDRVReopenState *state,
+                              BlockReopenQueue *queue, Error **errp)
+{
+    NFSClient *client = state->bs->opaque;
+    struct stat st;
+    int ret = 0;
+
+    if (state->flags & BDRV_O_RDWR && bdrv_is_read_only(state->bs)) {
+        error_setg(errp, "Cannot open a read-only mount as read-write");
+        return -EACCES;
+    }
+
+    /* Update cache for read-only reopens */
+    if (!(state->flags & BDRV_O_RDWR)) {
+        ret = nfs_fstat(client->context, client->fh, &st);
+        if (ret < 0) {
+            error_setg(errp, "Failed to fstat file: %s",
+                       nfs_get_error(client->context));
+            return ret;
+        }
+        client->st_blocks = st.st_blocks;
+    }
+
+    return 0;
+}
+
 static BlockDriver bdrv_nfs = {
     .format_name                    = "nfs",
     .protocol_name                  = "nfs",
@@ -499,6 +534,7 @@ static BlockDriver bdrv_nfs = {
     .bdrv_file_open                 = nfs_file_open,
     .bdrv_close                     = nfs_file_close,
     .bdrv_create                    = nfs_file_create,
+    .bdrv_reopen_prepare            = nfs_reopen_prepare,
 
     .bdrv_co_readv                  = nfs_co_readv,
     .bdrv_co_writev                 = nfs_co_writev,
-- 
1.9.1

Re: [Qemu-devel] [PATCH V3] block/nfs: cache allocated filesize for read-only files

[Jeff Cody]

On Thu, Aug 27, 2015 at 12:30:41PM +0200, Peter Lieven wrote:
> If the file is readonly its not expected to grow so
> save the blocking call to nfs_fstat_async and use
> the value saved at connection time. Also important
> the monitor (and thus the main loop) will not hang
> if block device info is queried and the NFS share
> is unresponsive.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
> v1->v2: update cache on reopen_prepare [Max]
> v2->v3: use cache only if cache.direct=off [Max]
> 

Reviewed-by: Jeff Cody <jcody@redhat.com>

Re: [Qemu-devel] [Qemu-block] [PATCH V3] block/nfs: cache allocated filesize for read-only files

[Max Reitz]

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On 27.08.2015 12:30, Peter Lieven wrote:
> If the file is readonly its not expected to grow so
> save the blocking call to nfs_fstat_async and use
> the value saved at connection time. Also important
> the monitor (and thus the main loop) will not hang
> if block device info is queried and the NFS share
> is unresponsive.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
> v1->v2: update cache on reopen_prepare [Max]
> v2->v3: use cache only if cache.direct=off [Max]
> 
>  block/nfs.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)

Reviewed-by: Max Reitz <mreitz@redhat.com>


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Re: [Qemu-devel] [PATCH V3] block/nfs: cache allocated filesize for read-only files

[Jeff Cody]

On Thu, Aug 27, 2015 at 12:30:41PM +0200, Peter Lieven wrote:
> If the file is readonly its not expected to grow so
> save the blocking call to nfs_fstat_async and use
> the value saved at connection time. Also important
> the monitor (and thus the main loop) will not hang
> if block device info is queried and the NFS share
> is unresponsive.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
> v1->v2: update cache on reopen_prepare [Max]
> v2->v3: use cache only if cache.direct=off [Max]
> 

Thanks,

Applied to my block branch:

git git://github.com/codyprime/qemu-kvm-jtc.git block

-Jeff