[pbs-devel] [PATCH proxmox-backup] mapped loop device: use read loop instead of read_exact

["Fabian Grünbichler" <f.gruenbichler@proxmox.com>]

since read_exact does not support short reads, which can easily happen if the
mapped image's EOF is not aligned with the request size.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---

Notes:
    reported on the forum:
    
    https://forum.proxmox.com/threads/problem-backing-up-using-backup-client.129347
    
    did a quick test reading from a mapped image full of random data, observed
    no performance difference..

 pbs-fuse-loop/src/fuse_loop.rs | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/pbs-fuse-loop/src/fuse_loop.rs b/pbs-fuse-loop/src/fuse_loop.rs
index 3d0ef123..7e780799 100644
--- a/pbs-fuse-loop/src/fuse_loop.rs
+++ b/pbs-fuse-loop/src/fuse_loop.rs
@@ -188,13 +188,20 @@ impl<R: AsyncRead + AsyncSeek + Unpin> FuseLoopSession<R> {
                             match self.reader.seek(SeekFrom::Start(req.offset)).await {
                                 Ok(_) => {
                                     let mut buf = vec![0u8; req.size];
-                                    match self.reader.read_exact(&mut buf).await {
-                                        Ok(_) => {
-                                            req.reply(&buf)
-                                        },
-                                        Err(e) => {
-                                            req.io_fail(e)
+                                    let mut read = 0;
+                                    let mut res = Ok(());
+                                    while read < req.size && res.is_ok() {
+                                        match self.reader.read(&mut buf).await {
+                                            Ok(0) => { break; },
+                                            Ok(n) => { read += n; },
+                                            Err(e) => { res = Err(e); },
                                         }
+                                    };
+                                    if let Err(e) = res {
+                                        req.io_fail(e)
+                                    } else {
+                                        buf.truncate(read);
+                                        req.reply(&buf)
                                     }
                                 },
                                 Err(e) => {
-- 
2.39.2