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Questions tagged [mmap]

mmap is a POSIX-compliant Unix system call that maps files or devices into memory.

mmap() creates a new mapping in the virtual address space of the calling process.

https://en.wikipedia.org/wiki/Mmap

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Identify flag in mmap function

void *mmap(void *addr, size_t length, int prot, int flags,int fd, off_t offset); I see call to mmap that prot=3 and flags=1 what does it mean about this buffer? ,How can I translate the flag that I see in man to number? Is the user can read/write…
parser1234
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Memory Mapping An Array to Another Array In C

I'm working with a loop with a very high iteration count, and so code within it will be quite performance critical. At some point in the loop I take a previously populated array of doubles and pass it to a function that for our purposes we can…
muke
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C mmap implementation for linux command

I have the following code which basically reproduce the functionality of the wc command in linux. My question is how I can rewrite the code using mmap? I know I can use struct stat sb; and then char *file_in_memory = mmap(NULL, sb.st_size,…
gameloverr2
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Extending a memory-mapped file in Python (Mac & Linux)

On Windows mmap'd files can be automatically extended on open, but this is not supported on UNIX-like systems: https://docs.python.org/3.7/library/mmap.html I have an existing set of classes that provide an append-only journal in Python using mmap,…
Kyle Downey
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Mmap, void pointer and type casting in C

I'm reading C on disk hash table code without knowing much about C or mmap but i know Golang. This piece of code confuses me. There are two structs like this. typedef struct HashTbl { void *data; ... } HashTbl; typedef struct Header { …
TomSawyer
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Insert image in blob in Sqlite

I am reading a directory for 600,000 images and wanting to store these images in a Sqlite DB. The DB structure is simply ID, IMAGE (blob). I'm not proficient in C++ so am figuring this out. First I open the DB file and setup the prepare statement…
Mudders
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shm_open segmentation fault and permission failed

I am new to Linux and i am trying to create a shared memory object which stores the collatz conjecture calculated in child process and prints it in parent process. I have already read the man pages for the commands. When I create the object it…
Shary
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How can we mmap a datastructure in python?

I have huge dictonary with some contents in memory which was created by searching similary sentence in a big wikipedia corpus . It has below dictonary format ,when i writed into a file its size was 150mb ,Now before writing it to file i want to…
star
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How to write into shared memory from a child process

I'm experimenting with child processes because this seems the only way to make an old C library run in parallel that cannot be used in threads. My minimal example writes three integer values into mapped memory. In the child process, I want to change…
gk017
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Create a new file to write to in C and initialize it as empty?

I want to open a new file and write a char array to it, but when I read back the contents of the file it has what I wrote to it followed by a bunch of garbage characters. I want to map the file to memory, but when I read the file back from that map,…
thebaconator
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Mmap problem -> segfault

I would like to share to use mmap. However it doesn't work, because I'm getting a segfault : int fdL = open("/dev/zero", O_RDWR | O_CREAT); int *ligneC = (int *) mmap(0, sizeof (int), PROT_READ | PROT_WRITE, MAP_SHARED, fdL, 0); *ligneC = 0; Where…
g123k
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mmap() causing segmentation fault in C

I'm pretty sure my mistake is very evident, but I just can't seem to find where the problem is. I'm learning how to use mmap() in C, everything looks correct to me, but I get a segmentation fault. Here is my code: int n=50; char * tab = mmap(NULL,…
CSstudZ
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Assembly sys_mmap linux x64 Bus failure

i opened a file (MEMORY) then i tried to use mmap syscall but after mmap called, i tried to use the allocated space and i got (Bus error) in Linux what is the problem !? i think something is wrong with my mmap parameters FORMAT ELF64…
ELHASKSERVERS
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Is it safe to modify file in place when replacement is same size as original

I want to do something similar to sed -i 's/abc/def/' file but without temp file. In my case match and replacement are of same length; is the following safe: fd = open(file, O_RDWR); fstat(fd, &sbuf); mm = mmap(0, sbuf.st_size, PROT_READ |…
Ani
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Is there a faster way to check if a txt file has two strings in it?

I am developing a script to read through logs on a log folder and check on each .txt log file: 1) if the log has the string 'FileData' and 2) if the log does not have the string 'Error in File Data' If this condition is met, it needs to read the…
Rafael Castelo Branco
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