Bug 1295007 - Non-GIO (POSIX) API call to save data truncates file to 0 bytes.
Non-GIO (POSIX) API call to save data truncates file to 0 bytes.
Product: Fedora
Classification: Fedora
Component: gvfs (Show other bugs)
x86_64 Linux
unspecified Severity high
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Assigned To: Ondrej Holy
Fedora Extras Quality Assurance
Depends On:
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Reported: 2015-12-31 13:22 EST by Benjamin Ariel Nava Martinez
Modified: 2016-12-20 12:31 EST (History)
3 users (show)

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2016-12-20 12:31:19 EST
Type: Bug
Regression: ---
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RHEL 7.3 requirements from Atomic Host:
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Description Benjamin Ariel Nava Martinez 2015-12-31 13:22:04 EST
Description of problem:
Whenever I save any file using an app that doesn't use GIO but rather POSIX to perform IO, the file ends up being truncated.

Version-Release number of selected component (if applicable):
Nombre      : gvfs
Arquitectur : x86_64
Epoch       : 0
Versión     : 1.26.2
Lanzamiento : 1.fc23
Tamaño      : 1.1 M
Repo        : @System
Desde repo  : updates
Resumen     : Backends for the gio framework in GLib
URL         : https://wiki.gnome.org/Projects/gvfs
Licencia    : GPLv3 and LGPLv2+ and BSD and MPLv2.0
Descripción : The gvfs package provides backend implementations for the gio
            : framework in GLib. It includes ftp, sftp, cifs.

Other relevant components:
Nombre      : fuse
Arquitectur : x86_64
Epoch       : 0
Versión     : 2.9.4
Lanzamiento : 3.fc23
Tamaño      : 220 k
Repo        : @System
Desde repo  : fedora
Resumen     : File System in Userspace (FUSE) utilities
URL         : http://fuse.sf.net
Licencia    : GPL+
Descripción : With FUSE it is possible to implement a fully functional filesystem in a
            : userspace program. This package contains the FUSE userspace tools to
            : mount a FUSE filesystem.

Nombre      : gvfs-fuse
Arquitectur : x86_64
Epoch       : 0
Versión     : 1.26.2
Lanzamiento : 1.fc23
Tamaño      : 37 k
Repo        : @System
Desde repo  : updates
Resumen     : FUSE support for gvfs
URL         : https://wiki.gnome.org/Projects/gvfs
Licencia    : GPLv3 and LGPLv2+ and BSD and MPLv2.0
Descripción : This package provides support for applications not using gio
            : to access the gvfs filesystems.

How reproducible:

Steps to Reproduce:
1. Open a file with an app that uses POSIX instead of GIO e.g. leafpad.
2. Attempt to write to the remote location.
3. File ends up being truncated to 0 bytes.

Actual results:
File is being truncated.

Expected results:
File is saved correctly.

Additional info:
Other relevant (external) bug reports:

https://bugzilla.redhat.com/show_bug.cgi?id=479199 (too old)
Comment 1 Ondrej Holy 2016-01-05 07:24:46 EST
Thanks for your bug report.

GIO API isn't fully compatible with POSIX and thus some operations might not be supported. However it is not definitely true that all "POSIX editors" doesn't work, I would say that most of the editors should work, e.g. nano works (first one I tried)...

It seems leafpad is doing something bit nonstandard, because it is using two file descriptors for writing:

open("/run/user/1000/gvfs/ftp:host=foo/bar", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 10
open("/run/user/1000/gvfs/ftp:host=foo/bar", O_WRONLY|O_CREAT|O_APPEND, 0666) = 11
lseek(11, 0, SEEK_END)                  = -1 ESPIPE (Illegal seek)
close(11)                               = 0
write(10, "foobar", 6)                  = -1 EOPNOTSUPP (Operation not supported)

As a result fuse calls vfs_write without O_APPEND, nor O_TRUNC:

vfs_open: /ftp:host=foo/bar
open_common: flags=101001
vfs_open: -> Success
vfs_open: /ftp:host=foo/bar
open_common: flags=102001
vfs_open: -> Success
vfs_release: /ftp:host=foo/bar
vfs_write: /ftp:host=foo/bar
vfs_write: flags=100001
vfs_write: -> Operation not supported
vfs_release: /ftp:host=foo/bar

This is not supported by the fuse daemon, because it might cause data corruptions due to the divergence of POSIX and GIO API, see:

I'm not sure if we can improve it somehow in GVfs, but I suppose it can be easily fixed in leafpad (e.g. adding O_APPEND for the first open)...
Comment 2 Ondrej Holy 2016-01-05 07:50:29 EST
There is also problem with invalidation ftp cache after writing, which might cause POSIX editors fails to read file content over fuse daemon after successful write:
Comment 3 Benjamin Ariel Nava Martinez 2016-01-05 17:11:59 EST
Thank you for your response, this is a leafpad-related bug then, if I understand correctly.
Comment 4 Fedora End Of Life 2016-11-24 09:37:57 EST
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Comment 5 Fedora End Of Life 2016-12-20 12:31:19 EST
Fedora 23 changed to end-of-life (EOL) status on 2016-12-20. Fedora 23 is
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