Readonly flag after error: why does Kernel detect an error?
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I'm debugging a C++ application running on Linux Embedded:
uname -r: 4.14.40
The application is downloading a file on an external flash SD card:
mount: sd-path type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
If a file doesn't exist, the file handler is opened with a w (full overwrite) flag, otherwise it is opened with r+ flag (append mode) so that the download may continue from the last downloaded sector.
What I'm observing is that if I power off the machine after starting to download the file, on reboot the SD is still available for write operation, while if I power off the machine a second time (while the file is being accessed in r+ mode) the SD is mounted again in readonly mode.
I suspect this happens because the Kernel detects an error and the SD is mounted in readonly mode, as specified by the mount options pasted above.
What I don't understand is why the r+ mode triggers the kernel error, which error is triggered (even a way to understand it would suffice) and if so how can I avoid the error. Is r+ inherently unsafe? Should I use other / additional flags for flash-specific IO operations?
Thank you for your time.
mount io c++ readonly flash-memory
asked Mar 14 at 13:08
phagiophagio
12
add a comment |
I'm debugging a C++ application running on Linux Embedded:
uname -r: 4.14.40
The application is downloading a file on an external flash SD card:
mount: sd-path type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
If a file doesn't exist, the file handler is opened with a w (full overwrite) flag, otherwise it is opened with r+ flag (append mode) so that the download may continue from the last downloaded sector.
What I'm observing is that if I power off the machine after starting to download the file, on reboot the SD is still available for write operation, while if I power off the machine a second time (while the file is being accessed in r+ mode) the SD is mounted again in readonly mode.
I suspect this happens because the Kernel detects an error and the SD is mounted in readonly mode, as specified by the mount options pasted above.
What I don't understand is why the r+ mode triggers the kernel error, which error is triggered (even a way to understand it would suffice) and if so how can I avoid the error. Is r+ inherently unsafe? Should I use other / additional flags for flash-specific IO operations?
Thank you for your time.
mount io c++ readonly flash-memory
asked Mar 14 at 13:08
phagiophagio
12
add a comment |
I'm debugging a C++ application running on Linux Embedded:
uname -r: 4.14.40
The application is downloading a file on an external flash SD card:
mount: sd-path type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
If a file doesn't exist, the file handler is opened with a w (full overwrite) flag, otherwise it is opened with r+ flag (append mode) so that the download may continue from the last downloaded sector.
What I'm observing is that if I power off the machine after starting to download the file, on reboot the SD is still available for write operation, while if I power off the machine a second time (while the file is being accessed in r+ mode) the SD is mounted again in readonly mode.
I suspect this happens because the Kernel detects an error and the SD is mounted in readonly mode, as specified by the mount options pasted above.
What I don't understand is why the r+ mode triggers the kernel error, which error is triggered (even a way to understand it would suffice) and if so how can I avoid the error. Is r+ inherently unsafe? Should I use other / additional flags for flash-specific IO operations?
Thank you for your time.
mount io c++ readonly flash-memory
asked Mar 14 at 13:08
phagiophagio
12
I'm debugging a C++ application running on Linux Embedded:
uname -r: 4.14.40
The application is downloading a file on an external flash SD card:
mount: sd-path type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
If a file doesn't exist, the file handler is opened with a w (full overwrite) flag, otherwise it is opened with r+ flag (append mode) so that the download may continue from the last downloaded sector.
What I'm observing is that if I power off the machine after starting to download the file, on reboot the SD is still available for write operation, while if I power off the machine a second time (while the file is being accessed in r+ mode) the SD is mounted again in readonly mode.
I suspect this happens because the Kernel detects an error and the SD is mounted in readonly mode, as specified by the mount options pasted above.
What I don't understand is why the r+ mode triggers the kernel error, which error is triggered (even a way to understand it would suffice) and if so how can I avoid the error. Is r+ inherently unsafe? Should I use other / additional flags for flash-specific IO operations?
Thank you for your time.
mount io c++ readonly flash-memory
mount io c++ readonly flash-memory
asked Mar 14 at 13:08
phagiophagio
12
asked Mar 14 at 13:08
phagiophagio
12
asked Mar 14 at 13:08
phagiophagio
12
asked Mar 14 at 13:08
phagiophagio
12
asked Mar 14 at 13:08
phagiophagio
12
12
add a comment |
add a comment |
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