__COPY_FROM_USER - Online Linux Manual PageSection : 9
Updated : June 2018
Source : Kernel Hackers Manual 2​.6​.
Note : Memory Management in Linux

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NAME__copy_from_user − Copy a block of data from user space, with less checking​.

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SYNOPSISunsigned long __copy_from_user(void * to, const void __user * from, unsigned long n);

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ARGUMENTSto Destination address, in kernel space​. from Source address, in user space​. n Number of bytes to copy​.

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CONTEXTUser context only​. This function may sleep​.

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DESCRIPTIONCopy data from user space to kernel space​. Caller must check the specified block with access_ok before calling this function​. Returns number of bytes that could not be copied​. On success, this will be zero​. If some data could not be copied, this function will pad the copied data to the requested size using zero bytes​. An alternate version − __copy_from_user_inatomic − may be called from atomic context and will fail rather than sleep​. In this case the uncopied bytes will *NOT* be padded with zeros​. See fs/filemap​.h for explanation of why this is needed​.

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