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Is there a Linux system call to create a “view” of a range of a file?
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Does Linux provide a system call which can create a "view" of a limited byte range of a backing file? I'm envisioning something that for example would act on an open file descriptor and either modify it or generate a new file descriptor where file offsets are relative to the beginning of the range and end at the end of the range.
The use-case would be to limit a non-cooperating subprocess to accessing only a particular portion of an input file.
linux files filesystems
edited 59 mins ago
Gilles
539k12810911606
asked 2 hours ago
llasramllasram
1163
New contributor
llasram is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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add a comment |
Does Linux provide a system call which can create a "view" of a limited byte range of a backing file? I'm envisioning something that for example would act on an open file descriptor and either modify it or generate a new file descriptor where file offsets are relative to the beginning of the range and end at the end of the range.
The use-case would be to limit a non-cooperating subprocess to accessing only a particular portion of an input file.
linux files filesystems
edited 59 mins ago
Gilles
539k12810911606
asked 2 hours ago
llasramllasram
1163
New contributor
llasram is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
See also Create a virtual file that is actually a command
– Gilles
59 mins ago
add a comment |
Does Linux provide a system call which can create a "view" of a limited byte range of a backing file? I'm envisioning something that for example would act on an open file descriptor and either modify it or generate a new file descriptor where file offsets are relative to the beginning of the range and end at the end of the range.
The use-case would be to limit a non-cooperating subprocess to accessing only a particular portion of an input file.
linux files filesystems
edited 59 mins ago
Gilles
539k12810911606
asked 2 hours ago
llasramllasram
1163
New contributor
llasram is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Does Linux provide a system call which can create a "view" of a limited byte range of a backing file? I'm envisioning something that for example would act on an open file descriptor and either modify it or generate a new file descriptor where file offsets are relative to the beginning of the range and end at the end of the range.
The use-case would be to limit a non-cooperating subprocess to accessing only a particular portion of an input file.
linux files filesystems
linux files filesystems
edited 59 mins ago
Gilles
539k12810911606
asked 2 hours ago
llasramllasram
1163
New contributor
llasram is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 59 mins ago
Gilles
539k12810911606
asked 2 hours ago
llasramllasram
1163
New contributor
llasram is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 59 mins ago
Gilles
539k12810911606
edited 59 mins ago
Gilles
539k12810911606
edited 59 mins ago
Gilles
539k12810911606
539k12810911606
asked 2 hours ago
llasramllasram
1163
New contributor
llasram is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 hours ago
llasramllasram
1163
asked 2 hours ago
llasramllasram
1163
1163
New contributor
llasram is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
llasram is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
llasram is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
See also Create a virtual file that is actually a command
– Gilles
59 mins ago
add a comment |
See also Create a virtual file that is actually a command
– Gilles
59 mins ago
See also Create a virtual file that is actually a command
– Gilles
59 mins ago
See also Create a virtual file that is actually a command
– Gilles
59 mins ago
add a comment |
1 Answer
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One way of doing this is to use a loop device. This approach does have two requirements which may make it less useful: you need to be root to set it up, and the non-cooperating subprocess must be able to write to a block device. Oh, and it doesn’t deal with conflicting changes.
To set the loop device up, run
losetup -o 1024 --sizelimit 2048 --show -f yourfile
replacing 1024, 2048 and yourfile with appropriate values — -o specifies the start offset, --sizelimit the size (counting from the offset). Note that sizelimit has to be a multiple of 512.
This will output the name of the loop device which has been set up; adjust the permissions as necessary, and give it to your non-cooperating sub-process. When you no longer need the device, delete it with
losetup -d /dev/loopN
replacing N as appropriate.
edited 2 hours ago
Stéphane Chazelas
307k57581938
answered 2 hours ago
Stephen KittStephen Kitt
173k24396471
Hmm, what do you mean with conflicting changes? Do you mean writes that come through the loop device not being in sync with direct writes to the backing file?
– ilkkachu
39 mins ago
add a comment |
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1 Answer
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1 Answer
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active
oldest
votes
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votes
active
oldest
votes
One way of doing this is to use a loop device. This approach does have two requirements which may make it less useful: you need to be root to set it up, and the non-cooperating subprocess must be able to write to a block device. Oh, and it doesn’t deal with conflicting changes.
To set the loop device up, run
losetup -o 1024 --sizelimit 2048 --show -f yourfile
replacing 1024, 2048 and yourfile with appropriate values — -o specifies the start offset, --sizelimit the size (counting from the offset). Note that sizelimit has to be a multiple of 512.
This will output the name of the loop device which has been set up; adjust the permissions as necessary, and give it to your non-cooperating sub-process. When you no longer need the device, delete it with
losetup -d /dev/loopN
replacing N as appropriate.
edited 2 hours ago
Stéphane Chazelas
307k57581938
answered 2 hours ago
Stephen KittStephen Kitt
173k24396471
Hmm, what do you mean with conflicting changes? Do you mean writes that come through the loop device not being in sync with direct writes to the backing file?
– ilkkachu
39 mins ago
add a comment |
One way of doing this is to use a loop device. This approach does have two requirements which may make it less useful: you need to be root to set it up, and the non-cooperating subprocess must be able to write to a block device. Oh, and it doesn’t deal with conflicting changes.
To set the loop device up, run
losetup -o 1024 --sizelimit 2048 --show -f yourfile
replacing 1024, 2048 and yourfile with appropriate values — -o specifies the start offset, --sizelimit the size (counting from the offset). Note that sizelimit has to be a multiple of 512.
This will output the name of the loop device which has been set up; adjust the permissions as necessary, and give it to your non-cooperating sub-process. When you no longer need the device, delete it with
losetup -d /dev/loopN
replacing N as appropriate.
edited 2 hours ago
Stéphane Chazelas
307k57581938
answered 2 hours ago
Stephen KittStephen Kitt
173k24396471
Hmm, what do you mean with conflicting changes? Do you mean writes that come through the loop device not being in sync with direct writes to the backing file?
– ilkkachu
39 mins ago
add a comment |
One way of doing this is to use a loop device. This approach does have two requirements which may make it less useful: you need to be root to set it up, and the non-cooperating subprocess must be able to write to a block device. Oh, and it doesn’t deal with conflicting changes.
To set the loop device up, run
losetup -o 1024 --sizelimit 2048 --show -f yourfile
replacing 1024, 2048 and yourfile with appropriate values — -o specifies the start offset, --sizelimit the size (counting from the offset). Note that sizelimit has to be a multiple of 512.
This will output the name of the loop device which has been set up; adjust the permissions as necessary, and give it to your non-cooperating sub-process. When you no longer need the device, delete it with
losetup -d /dev/loopN
replacing N as appropriate.
edited 2 hours ago
Stéphane Chazelas
307k57581938
answered 2 hours ago
Stephen KittStephen Kitt
173k24396471
One way of doing this is to use a loop device. This approach does have two requirements which may make it less useful: you need to be root to set it up, and the non-cooperating subprocess must be able to write to a block device. Oh, and it doesn’t deal with conflicting changes.
To set the loop device up, run
losetup -o 1024 --sizelimit 2048 --show -f yourfile
replacing 1024, 2048 and yourfile with appropriate values — -o specifies the start offset, --sizelimit the size (counting from the offset). Note that sizelimit has to be a multiple of 512.
This will output the name of the loop device which has been set up; adjust the permissions as necessary, and give it to your non-cooperating sub-process. When you no longer need the device, delete it with
losetup -d /dev/loopN
replacing N as appropriate.
edited 2 hours ago
Stéphane Chazelas
307k57581938
answered 2 hours ago
Stephen KittStephen Kitt
173k24396471
edited 2 hours ago
Stéphane Chazelas
307k57581938
edited 2 hours ago
Stéphane Chazelas
307k57581938
edited 2 hours ago
Stéphane Chazelas
307k57581938
307k57581938
answered 2 hours ago
Stephen KittStephen Kitt
173k24396471
answered 2 hours ago
Stephen KittStephen Kitt
173k24396471
answered 2 hours ago
Stephen KittStephen Kitt
173k24396471
173k24396471
Hmm, what do you mean with conflicting changes? Do you mean writes that come through the loop device not being in sync with direct writes to the backing file?
– ilkkachu
39 mins ago
add a comment |
Hmm, what do you mean with conflicting changes? Do you mean writes that come through the loop device not being in sync with direct writes to the backing file?
– ilkkachu
39 mins ago
Hmm, what do you mean with conflicting changes? Do you mean writes that come through the loop device not being in sync with direct writes to the backing file?
– ilkkachu
39 mins ago
Hmm, what do you mean with conflicting changes? Do you mean writes that come through the loop device not being in sync with direct writes to the backing file?
– ilkkachu
39 mins ago
add a comment |
llasram is a new contributor. Be nice, and check out our Code of Conduct.
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llasram is a new contributor. Be nice, and check out our Code of Conduct.
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See also Create a virtual file that is actually a command
– Gilles
59 mins ago