Opened 13 years ago
Last modified 5 years ago
#9485 closed defect
shared folders problem: IO to overwritten file (XP Home host) — at Initial Version
Reported by: | Kris Thielemans | Owned by: | |
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Component: | guest additions | Version: | VirtualBox 4.1.2 |
Keywords: | shared folder IO | Cc: | |
Guest type: | Linux | Host type: | Windows |
Description
Hi I am using XP Home Edition (fully patched) as host, running Ubuntu 11.4 as guest (but similar problems with Ubuntu 10.4) on VBox 4.1.2.
I encounter problems in a rather specific set of circumstances when using shared folders (a discussion of this problem is on the forum http://forums.virtualbox.org/viewtopic.php?f=3&t=44056&p=198273#p198223)
My program creates a new file, writes to the file, and then reads what it wrote itself. The read then fails if the file already exists (on a shared folder), but works fine if the file didn't exist.
For my latest tests, the shared folder is on d:\tmp (newly created) and permissions set to "Full Access" for everyone (set using Safe Mode). VBox runs as normal user "kris". I mounted the folder in Ubuntu as follows:
mkdir /home/kris/tmpmntD sudo mount -t vboxsf -o uid=1000,gid=1000,rw dtmp /home/kris/tmpmntD
An example C program showing the problem:
#include <stdio.h> #include <stdlib.h> #include <string.h> int main() { char buffer[1024]; int ret; /* Open file test.txt in current dir as "read-write new binary file" */ FILE *fptr= fopen("test.txt","wb+"); if (fptr==NULL) { fprintf(stderr, "Error opening file\n"); exit(1); } memset(buffer,'a',1024); ret = fwrite(buffer, 1, 1024, fptr); printf("fwrite return (should be 1024): %d\n", ret); ret=fseek(fptr, 512, 0); printf("fseek return (should be 0): %d\n", ret); ret=fread(buffer, 1, 512, fptr); printf("fread return (should be 512): %d\n", ret); /* return from main checking if fread did read 512 bytes */ return ret==512 ? 0 : 1; }
When I run this program somewhere in a new directory on a shared-folder, the first time it works fine and reports:
write return (should be 1024): 1024 fseek return (should be 0): 0 fread return (should be 512): 512
This creates a file test.txt (of size 1024). Rerunning the program now fails as test.txt already exists:
fwrite return (should be 1024): 1024 fseek return (should be 0): 0 fread return (should be 512): 0
It works fine again once I remove test.txt, or of course if I run this program creating a file in a folder in the disk image. (It also fails if the existing file test.txt has zero size).
Note that the use of the "w+" flag for fopen is crucial for the bug to appear. If I use "r+", the program always succeeds.
vbox.log