LittleFS fopen in 'w' mode removes existing file

[janjongboom]

From https://os.mbed.com/questions/79863/LittleFileSystem-fopenfilew-does-remove-/

According to the C++ fopen documentation at http://www.cplusplus.com/reference/cstdio/fopen/ if 'mode' is "w" and the filename points to an existing file, the contents of the existing file are cleared.

FATFileSystem does have this behaviour but LittleFileSystem does not seem to. Here's some example code....

char * filename = "/fs/eventlog.bin";
FILE *fd = fopen(filename,"w");
fclose(fd);
struct stat stat_buf;
stat(filename, &stat_buf);
ASSERT(stat_buf.st_size!=0,"file size should be zero after opening");

When the underlying filesystem is LittleFileSystem and if the file already exists and it not empty, this asserts since the filesize is not changed on fopen.

Obviously a workaround is to use the remove method (or possibly a zero-length write?)

[janjongboom]

@geky

[ciarmcom]

ARM Internal Ref: IOTMORF-1909

[geky]

Ah! This is the same as this issue, just hidden under a few layers: littlefs-project/littlefs#7

Here's a patch that will fix this: #5832

[NeilMacMullen]

@geky thanks - only just saw this.