# Re: [PATCH] Seek back to current filepos when mmap()ing with NO_MMAP 4 messages from 2006-11-15 to 2006-11-15. Participants: Johannes Schindelin, Alex Riesen, Morten Welinder. Thread: https://gitlist.dev/t/43413 ## Johannes Schindelin, 2006-11-15 16:27 Subject: [PATCH] Seek back to current filepos when mmap()ing with NO_MMAP Message-ID: URL: https://gitlist.dev/e/Pine.LNX.4.63.0611151727000.13772%40wbgn013.biozentrum.uni-wuerzburg.de ``` "git-index-pack --fix-thin" relies on mmap() not changing the current file position (otherwise the pack will be corrupted when writing the final SHA1). Meet that expectation. Signed-off-by: Johannes Schindelin --- Sorry for not catching that earlier. It only affects platforms where you have to set NO_MMAP=YesPlease, anyway. compat/mmap.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) diff --git a/compat/mmap.c b/compat/mmap.c index 55cb120..a4d2e50 100644 --- a/compat/mmap.c +++ b/compat/mmap.c @@ -7,6 +7,7 @@ void *gitfakemmap(void *start, size_t length, int prot , int flags, int fd, off_t offset) { int n = 0; + off_t current_offset = lseek(fd, 0, SEEK_CUR); if (start != NULL || !(flags & MAP_PRIVATE)) die("Invalid usage of gitfakemmap."); @@ -39,6 +40,11 @@ void *gitfakemmap(void *start, size_t le n += count; } + if (current_offset != lseek(fd, current_offset, SEEK_SET)) { + errno = EINVAL; + return MAP_FAILED; + } + return start; } -- dummy-dirty ``` ## Morten Welinder, 2006-11-15 18:26 Subject: Re: [PATCH] Seek back to current filepos when mmap()ing with NO_MMAP Message-ID: <118833cc0611151026q25fb6eeeid3a74e20498f00d@mail.gmail.com> URL: https://gitlist.dev/e/118833cc0611151026q25fb6eeeid3a74e20498f00d%40mail.gmail.com In-Reply-To: ``` Using xmalloc in there seems wrong. A plain malloc would do and the error would be returned back to the mmap caller. ``` ## Johannes Schindelin, 2006-11-15 18:32 Subject: Re: [PATCH] Seek back to current filepos when mmap()ing with NO_MMAP Message-ID: URL: https://gitlist.dev/e/Pine.LNX.4.63.0611151932230.13772%40wbgn013.biozentrum.uni-wuerzburg.de In-Reply-To: <118833cc0611151026q25fb6eeeid3a74e20498f00d@mail.gmail.com> ``` Hi, On Wed, 15 Nov 2006, Morten Welinder wrote: > Using xmalloc in there seems wrong. A plain malloc would do and the > error would be returned back to the mmap caller. I did not touch that code at all in this patch. Ciao, Dscho ``` ## Alex Riesen, 2006-11-15 19:06 Subject: Re: [PATCH] Seek back to current filepos when mmap()ing with NO_MMAP Message-ID: <81b0412b0611151106k45ee03ekd8a3a04173f618c3@mail.gmail.com> URL: https://gitlist.dev/e/81b0412b0611151106k45ee03ekd8a3a04173f618c3%40mail.gmail.com In-Reply-To: ``` On 11/15/06, Johannes Schindelin wrote: > > "git-index-pack --fix-thin" relies on mmap() not changing the current > file position (otherwise the pack will be corrupted when writing the > final SHA1). Meet that expectation. > Thanks! I was wondering for some considerable time why the hell t5500-fetch-pack fails. BTW, I extended error handling in that mmap. Dunno why. Signed-off-by: Alex Riesen commit 40ed0644ca8d250f716f49a5c3e027aa2c1d3167 Author: Alex Riesen Date: Wed Nov 15 19:55:06 2006 +0100 Seek back to current filepos when mmap()ing with NO_MMAP, eh improved "git-index-pack --fix-thin" relies on mmap() not changing the current file position (otherwise the pack will be corrupted when writing the final SHA1). Meet that expectation. Signed-off-by: Johannes Schindelin Signed-off-by: Alex Riesen diff --git a/compat/mmap.c b/compat/mmap.c index 55cb120..c6d5cfe 100644 --- a/compat/mmap.c +++ b/compat/mmap.c @@ -6,7 +6,8 @@ void *gitfakemmap(void *start, size_t length, int prot , int flags, int fd, off_t offset) { - int n = 0; + int n = 0, err = 0; + off_t current_offset = lseek(fd, 0, SEEK_CUR); if (start != NULL || !(flags & MAP_PRIVATE)) die("Invalid usage of gitfakemmap."); @@ -18,8 +19,8 @@ void *gitfakemmap(void *start, size_t le start = xmalloc(length); if (start == NULL) { - errno = ENOMEM; - return MAP_FAILED; + err = ENOMEM; + goto unseek; } while (n < length) { @@ -31,14 +32,22 @@ void *gitfakemmap(void *start, size_t le } if (count < 0) { - free(start); - errno = EACCES; - return MAP_FAILED; + err = EACCES; + goto unseek; } n += count; } +unseek: + if (current_offset != lseek(fd, current_offset, SEEK_SET)) + err = EINVAL; + + if (err) { + free(start); + start = MAP_FAILED; + errno = err; + } return start; } ```